Bulletin of The Iwate Agricultural Research Center No.13
Summary

Studies on the Pathogen, Epidemiology and Control of Gentian Brown Leaf Spot Caused by Mycochaetophora gentianae.
Syuuichi NEKODUKA
Brown leaf spot disease causes significant economic losses on gentian. This report summarizes results from studies conducted in a total of seven years (2000–2003 and 2007–2009) at Iwate Agricultural Research Center in Kitakami, Iwate Prefecture, with special reference to the pathogen, epidemiology and control of the disease.

Ⅰ Symptoms and epidemics of the disease
1. Early leaf symptoms on gentian cv. Jobanni and cv. Ihatovo include minute, grayish white lesions on the upper surface. The lesions progressively enlarge to ca. 5mm in diameter with yellowish marginal area, and subsequently become brown and rotten. Cv. Ihatovo developes the lesions on both sides of the leaf. Symptoms on cv. Aoi-kaze and cv. Koromokawa-princess, which are brown, circular and conspicuous, are different from the typical symptoms (grayish white, powdery lesions) on cv. Jobanni.
2. Field observations revealed epidemiologic characteristics of the disease as follows. Lesions first appeared in early August, gradu-ally increased toward mid-August, and rapidly between late-August to early-September. The disease was more serious on plant leaves facing between two rows, and on the lower leaves. In the field, lesions were at first found sporadically, and then increased to neighboring healthy plants.

Ⅱ Taxonomic position of the causal fungus
1. The causal fungus (K18) isolated from Gentiana triflora was identified as Mycochaetophora gentianae because of its identity to the the ex-type strain (MAFF 239231) in terms of cultural characteristics, pathogenicity, conidial morphology, and genetic similarity as follows.
(1) Cultural characteristics: the isolate grew at temperatures from 5 to 30°C, but did not grow above 32.5°C with an optimum at ca. 20°C.
(2) Pathogenicity: inoculation tests showed that the isolate produced lesions on G. triflora cv. Ashiro-no-aki, but not G. scabra cv. Ashiro-no-sawakaze.
(3) Morphological characteristics: the isolate produced besom-like sporophores on diseased leaves. Conidial morphologies were almost identical between the two isolates except for their shape of the apex.
(4) Genetic similarity: ITS sequence was identified between the two isolates with 99.6% similarity (two nucleotides difference).
2. Microscopic observations revealed that conidia of M. gentianae were produced blasticaly from short conidiophores and detached in a schizolytic manner, leaving unthickened and inconspicuous scars on the conidiogenous cells.
3. Phylogenetic analyses revealed the phylogenetic position of M. gentianae and its allied fungi, Pseudocercosporella-like hypho-mycetes in conidiogenesis and conidial morphology.
(1) Phylogenetic analyses using 3 rDNA sequences combined (SSU + LSU + 5.8S rDNA) indicated that M. gentianae was a mem-ber of the Helotiales-Rhytismatales clade with strong support (BP = 88%) and placed in proximity to the helotialean families, but failed to characterize the position of M. gentianae at the family level.
(2) Molecular and morphological data clearly showed that M. gentianae had affinity with three helotialean, Pseudocercosporella-like hyphomycetes (Helgardia, Rhexocercosporidium, Rhynchosporium) but that the fungus was distinct from these fungi.
(3) ITS phylogeny indicated that M. gentianae was also related to Cadophora, Leptodontidium, and Pyrenopeziza brassicae, as well as helotialean Pseudocercosporella-like hyphomycetes.

Ⅲ Physiological characteristics of the causal fungus
1. Conidium germination
(1) Conidia germinated at temperatures between 10–30°C with an optimal range between 20–25°C and at pH 3–9 with an optimal range between pH4–9. There was no difference in the percentage of conidium germination between on WA and potato dextrose agar (PDA).
(2) Relative humidity (RH) over 99% was required for conidium germination (the optimum was 100% RH). The rate of conidium germination was higher in dry-water than in free-water treatment at 100% RH.
2. Mycelial growth
(1) Colony growth of the fungus was vigorous on PDA, potato carrot agar (PCA), V8-juice agar, oat meal agar, malt extract agar, and yeast extract agar. Colonies grown on both V8-juice agar and oat meal agar were yellow to olive. Felty colonies developed on yeast extract agar. The fungus failed to produce conidia on these tested media.
(2) Colony grew on PDA adjusted at pH 3–10 with an optimal range between pH4–10.
3. Induction of conidium formation
(1) PCA slide culture induced conidium (sporophore) formation. Sporophores were formed on the mycelia grown over the surface of cover-glass and on extended growth beyond cover-glass. Additionally, sporophore formation was induced by removing cover-glass or cellophane overlaid on PCA-slide culture.
(2) Conidial suspension > 105 conidia/ml was obtained when potato-carrot broth inoculated with mycelial blocks was shaken at 120rpm at 15°C for 5d.

Ⅳ Epidemiology
1. Effect of inoculum density, temperature, leaf wetness duration, and leaf age on infection of the causal fungus with conidia Inoculation tests with conidial suspension revealed that disease incidence was affected by inoculum density, temperature, and leaf wetness duration.
(1) Inoculum density: disease incidence increased with increasing inoculum density. Even an inoculum density as low as 102 co-nidia/ml could produce lesions. Logarithm of inoculum density was closely correlated to disease incidence (R2 = 0.840).
(2) Temperature: temperatures between 15–25°C were conducive to the disease, but those below below 10°C did not cause any le-sions.
(3) Leaf wetness duration: disease incidence increased with the increasing duration of leaf wetness (36–72h), but no lesions occur when leaf wetness lasted less than 24 h. Leaf wetness duration required for developing more than 50% of disease incidence was 60, 48, and 36 h at 15, 20, and 25°C, respectively.
(4) Leaf age: disease incidence on the top (youngest) leaves was lower than on the middle and bottom leaves (oldest), although analysis of variance indicated that the F value of leaf age was lower than that of temperature and leaf wetness duration.
2. Invasion of gentian leaves
(1) On gentian leaves, conidia germinated well in the range from 20°to 25°C. After 48h of incubation, all conidia germinated at 15°–25°C.
(2) Lesions that developed 7d after inoculation had one to several germinated conidia. The conidia generally had germ tubes from one or both ends of the cells, but some germinated from the middle of conidial cells. Appressoria were usually formed at the tip of germ tubes and varied in shape, color and size, i.e., they were often clavate to ellipsoid, hyaline to pale brown and 8–10 × 5–8 µm. It is notable that appressoria were formed near the grooves on the boundary of epidermal cells. Hyphal mat developed under epidermal cells of the lesions.
(3) Appressorium formation was markedly influenced by temperature and leaf wetness duration. More appressoria were formed at higher temperatures (15–25°C) with extended duration of leaf wetness (24–72h). At 48-h leaf wetness, the rate of appressori-um formation was 0, 8, 26, and 73% at 10, 15, 20, and 25°C, respectively.
3. Latent period for disease development
(1) When inoculated plants were maintained in a moist chamber at 25°C, minute lesions appeared 7d after inoculation, and then developed conspicuously 14d after inoculation.
(2) The latent period for disease development was longer at lower temperature (15–20°C) as compared with 25°C.
4. Conidium formation and dispersion on diseased leaves
Sporophores were produced on diseased leaves when they were incubated in a moist chamber for several days. The sporophore formation was affected by (1) disease severity of the leaf tissue, (2) growth stage of host plants, (3) temperature, and (4) relative humidity (RH). Conidia produced on diseased leaves were easily dispersed into water drop.
(1) Disease severity of the leaf tissue: sporophores were formed exclusively on brown and rotten lesions.
(2) Growth stage of host plants: the rate of sporophore formation on diseased leaves was higher in the early stage (May–June) and in the blooming stage (September–October) than in the budding stage (July–August).
(3) Relative humidity (RH): over 99% RH (the optimum 100% RH) was required for sporophore formation; RH below 86.5%, however, prevented even conidiophore formation.
(4) Conidial dispersion: conidia were dispersed from the sporophores into water drop. The number of conidia in the droplet was the highest at 20°C (6.2×102 conidia/ml) when diseased leaves were incubated in the humidity for 3 days; it was 4.2×104 conidia/ml when incubated at 25°C for 4 days.
5. Primary inoculum source
(1) Neither conidiophore nor sporophore was found on overwintered, infected leaves in an unglazed pot. Conidiophores emerged from the overwinetered, infected leaves when they were incubated into a moist chamber at 15°C, and subsequently sporophores developed with numerous conidia. Sporophores were formed on the overwintered leaves sampled by July; the frequency of the sporophore formation was the highest on the leaves sampled in April, then became lower thereafter with increasing air temperature. Sprophores were not found in August.
(2) Plants were diseased when planted in spring in the soil infested the previous year or when debris of diseased plants had been laid on the soil surface the previous fall. Even though the diseased debris was removed before planting gentians, lesions devel-oped on the plants. The removal of the debris decreased the number of lesions. The lesions were more abundant on the lower leaves than upper leaves.
(3) Cultures were obtained from lesions on inoculated plants using the debris of the overwintered diseased leaves and used for PCR detecting with SSU rDNA. The size of PCR products agreed with that of the original culture (isolate K18) with a length of ca. 1600 bp but differed from that of the reference culture (isolate J4) with ca. 1000 bp.
(4) When healthy gentians were planted in soil contaminated with conidial suspension, the disease never occurred in 2008, but only a slight number of lesions were found in 2009. Further studies are required for elucidating the soil-born nature of the pathogen.
6. Infection process in commercial fields
(1) Four-year exposure tests (2001–2003 in Hanamaki and 2008 in Kitakami) revealed that the infection of the causal fungus started in late June to early July and continued until September in the commercial fields. Inoculum potential was highest in early July before disease occurrence, and after disease occurrence, it culminated in mid to late August. Disease incidence of plants exposed in both periods tended to be enhanced by many rainy days.
(2) Multiple regression analysis was conducted using dataset of disease incidence as dependent variable and climatic factors as ex-planatory variables obtained from the four-year exposure tests. The results showed that disease incidence was strongly corre-lated with a total number of two consecutive rainy days. Correlation coefficient (R2) was 0.366 in June–July (Y1) and 0.640 in August–September (Y2).
(3) Latent period inferred from the dataset was ca. 14 days in 2002 and 20–38 days in 2003 on assumption that infection occurred on the first rainy day.

Ⅴ Susceptability of G. triflora and G. scabra to M. gentianae
1. Inoculation tests for seedlings showed that M. gentianae strain K18 (isolated from G. triflora) and MAFF 239231 (isolated from G. scabra) caused lesions on all six G. triflora cultivars but failed to infect G. scabra cv. Aruta.
2. Inoculation tests for cut plants showed that M. gentianae strain K18 caused lesions on all ten G. triflora cultivars, as well as cv. Lovely-ashiro and cv. New-hybrid-ashiro (both origins unknown), but failed to infect two G. scabra cultivars (cv. Ashiro-no-sawakaze and cv. Aruta) and an interspecific hybrid between G. triflora and G. scabra, cv. Arubireo.
3. Parents of the interspecific hybrid cv. Arubireo, G. triflora cv. Ba was susceptible but G. scabra cv. OK was resistant for the causal fungus. These results indicate that the resistance of G. scabra is inherited dominantly.

Ⅵ Disease control
1. Fungicide application tests in gentian field showed that basic copper sulfate, TPN, and kresoxym-methyl were highly effective as reported in the previous study, and the present study revealed the effectiveness of thiuram.
2. The relationship between TPN-application timing and the control efficacy was evaluated for three year times to examine infection periods in the field. The results showed that any of the application between late June and late July could control the disease with two consecutive applications. In 2002 and 2003, the application around early July was effective, which agreed with the fact that inoculum potential culminates in early July. Four consecutive application from late June to late July with 10 day intervals was su-perior to two consecutive applications around early July, in that the latter method failed to control disease development until October, despite of controlling perfectly until August. In conclusion, fungicide application for the disease control should be made con-secutively in late June–late July (the rainy season) in Iwate.

Ⅶ The life cycle of the causal fungus and disease ecology in Iwate
Results revealed that the brown leaf spot fungus on gentian was anamorphic in the field. Life cycle of the fungus and disease epi-demiology in Iwate are summarized as follows.
1. Life cycles
A primary inoculum source is conidia formed on overwintered, infected leaves in the rainy season (late June to late July). Minute lesions appear sporadically on leaves in early August. The diseased leaves become secondary inoculum source and form conidia (sporophores) on the lesions. The conidia are dispersed into rain drops, which splash the conidia widely. The causal fungus over-winters as the hyphal mat under leaf epidermal cells. Overwintered, infected leaves serve as the primary inoculum source the fol-lowing year.
2. The primary inoculum source
Overwintered, infected leaves as the primary infection source, form sporophores under the weather conditions in which temperature reaches about 15°C and leaf wetness duration continues for several days. In Iwate, primary infection continues between late June and late July, and infection frequency is higher around early July, i.e., just before the rainy season.
3. Infection and disease development
Leaf wetness duration is a limiting factor for conidial infection. Long period of leaf wetness (more than 36h) are required as com-pared to other general plant pathogens. Temperature for conidial infection ranges from 15 to 25°C, and higher temperature allows rapid infection within short duration of leaf wetness.
Germinated conidia form appressoria on the surface of gentian leaves. Appressorium formation is promoted by high temperature and long leaf wetness duration. Appressorium may form infection hypha for invasion under epidermis of the leaves. Further studies still remain to clarify an invasion mode.
Latent period for disease development is affected by temperatures. At 25°C, lesions obviously develop ca. 14d after inoculation, although the period tends to extend at lower temperatures. High temperatures tend to stimulate disease development rapidly, which agrees with field observations that lesions usually appear in early August. The appearance may be promoted by rapidly increase in temperature after the end of the rainy season.
4. Secondary inoculum source
Sporophores are formed on diseased leaves when the lesion tissues turn brown and rotten and when humidity reaches > 99% RH (the optimum 100% RH). Long duration of leaf wetness leads to an increase in sporophore formation. Conidia produced on dis-eased leaves are dispersed into rain drops, and the droplet splashes and helps the pathogen infect leaves. Primary lesions appearing in the fields in early August, even though still sporadic, could provide sufficient inoculum in the late phase of epidemics.
Studies on the Epidemiology and Control of Cucumber Black Root Rot Caused by Phomopsis sclerotioides in Iwate Prefecture
Yasuya IWADATE
 Black root rot of cucumber (Cucumis sativus) caused by Phomopsis sclerotioides is a serious greenhouse disease in many countries. P. sclerotioides is soil-borne and infects cucurbit vegetables. Since 2002, the disease has been observed in outdoor-cultivated cucumber grafted on pumpkin rootstock in Iwate Prefecture, Japan, causing severe economic losses. However, epidemiological information on this pathogen is limited, and an effective control method for outdoor-cultivated cucumber is warranted. The four main objectives of this study were as follows: (1) to describe the occurrence of cucumber black root rot and the extent of damage caused by P. sclerotioides in Iwate Prefecture; (2) to investigate the characteristics of the pathogen and its epidemiology; (3) to develop control methods for cucumber black root rot by using a resistant rootstock and/or chloropicrin fumigants; and (4) to evaluate the control method against cucumber black root rot through the application of soil pH amendments by using a converter slag. The results obtained from this study are briefly described below.

1. The occurrence of cucumber black root rot and the extent of damage caused by P. sclerotioides in Iwate Prefecture
 Black root rot on outdoor-cultivated cucumber grafted on pumpkin rootstock was found in three out of the 58 municipalities of Iwate Prefecture in 2002. Since then, the incidence of black root rot in cucumber crops has increased, affecting 16 out of the 33 amalgamated municipalities in 2012 that contain 29 ex-municipalities. The disease causes sudden wilting of plants, usually immediately before the harvest period, thus resulting in severe losses in the marketable yield. At first, infected plants show slight wilting during periods of high evapotranspiration during the day, although these show recovery at night. Once wilting is observed, most of the infected plants die within few days. In fully wilted plants, the roots become brown to black coloration and finally rot. In addition, most of the rootlets and root hairs fall off. At the last stage of the disease, pseudomicrosclerotia and pseudostromata form on the radicular surface of the plants. Weather conditions largely influence the development and progression of the disease. Wilt symptoms tend to be more severe during below-average summer temperatures such as that during 2003 compared to extraordinarily hot summers such as that in 2010. It has been suggested that high temperatures generally weaken the pathogen and below-average summer temperatures induce plant stress.
 The disease is frequently found in continuously cropped cucumber fields, as well as in new fields. The results of this study suggest that the pathogen has further spread across Iwate Prefecture, possibly through the transport of contaminated soil by footwear, plant materials, or machinery. Therefore, it is important to prevent the transfer of infested soil and contaminated equipment to uninfested fields. The results of the survey questionnaire collected from 2007 to 2011 revealed that only approximately 40% of cucumber farmers have engaged in fumigation of the infested fields by using chloropicrin, whereas farmers of approximately 60% of infested fields have continued cucumber cultivation without any disinfestation treatment.
 Sudden wilting was caused not only by cucumber black root rot but also by other plant diseases and pests. Sudden wilting caused by other plant diseases and pests were attributed to the following factors: (1) superinfection with Cucumber mosaic virus (CMV) and Zucchini yellow mosaic virus (ZYMV); (2) Gummy stem blight; (3) Fusarium wilt; (4) Phytophthora rot; (5) root knot; and (6) Monosporascus root rot. To the author's knowledge, for the first time in Japan, Monosporascus root rot of cucumber has been confirmed. This disease was observed in the summer to autumn cucumber harvest period of 2006 in the open fields of Iwate Prefecture. The causal fungus was identified as Monosporascus cannonballus, based on its morphological features and confirmed using polymerase chain reaction (PCR) with a M. cannonballus-specific primer pair. Furthermore, the unique root symptom included the presence of perithecia in the brown lesions; thus, it is easy to distinguish Monosporascus root rot from Phomopsis black root rot. Monosporascus root rot exclusively occurred in cucumber roots and was not found in those grafted on pumpkin rootstocks.

2. Characteristics and epidemiology of P. sclerotioides
 Cultural characteristics of P. sclerotioides were as follows: (1) the fungus grew on potato dextrose agar (PDA) at a temperature range of 10–30°C, but did not thrive above 32.5°C (optimal range: 20–25°C); (2) in vitro mycelial growth of the pathogen was optimal at a pH range of 4.0–5.0 and decreased at higher or lower pH levels; and (3) the fungus was killed after incubation at 35°C for 5–7 days, at 37.5°C for 4–5 days, and at 40°C for 2–4 days.
 Disease development of cucumber black root rot was as follows: (1) temperatures between 20 and 25°C were conducive to disease development, whereas at 30°C, it was suppressed; (2) symptoms of wilting were enhanced by drought; (3) the disease could occur by inoculation at an extremely low density, even at 0.01% (w/w) of the naturally infested soil; and (4) in most cases, the pathogen could thrive up to a soil depth of at least 40 cm in naturally infested fields.
 Long-term survival of pseudostromata and pseudomicrosclerotia on the hypocotyl or radicular residual tissues does not occur in dry soil conditions, whereas humid conditions facilitate its long-term survival in soil. It has been previously shown that pseudostromata and pseudomicrosclerotia may play important roles as survival structures in the soil.

3. Control method by using resistant rootstock and/or chloropicrin fumigants against cucumber black root rot
 To prevent cucumber black root rot, several Cucurbitaceae plants were examined as resistant rootstocks for grafting cucumber plants, and Cucurbita ficifolia and Benincasa hispida were found to be effective. C. ficifolia is highly compatible to cucumber and is easy to graft because of its thick hypocotyl. On the other hand, some cultivars of B. hispida showed inadequate adaptability for grafting cucumber plants. Thus, C. ficifolia can be used as the resistant rootstock for grafting cucumber. However, C. ficifolia, a bloom type rootstock, cannot be extensively used as the resistant rootstock for cucumber grafting in commercial fields because the Japanese market preference is for bloomless fruits.
 Soil fumigants such as chloropicrin (298.5 L a.i./ha), dazomet (294 kg a.i./ha), metham sodium (180 L a.i./ha), and fluazinam (15 kg a.i./ha) were evaluated for efficacy in naturally infested fields. On the basis of the significant reduction of sudden wilting, chloropicrin was selected for subsequent experiments and used to develop an effective control scheme. A high level of efficacy against cucumber black root rot was observed in all chloropicrin dosage forms: chloropicrin solution (product name: Chloropicrin), chloropicrin emulsion (Chlopic-flow), chloropicrin tablet (Chloropicrin jouzai), and chloropicrin tape (Chlopic-tape). Partial fumigation (injection into polyethylene-mulched beds) resulted in its adequate control, which was better than that by overall fumigation in the fields. After partial fumigation, it was essential to position the cucumber seedlings in the center of the beds because the fumigation process only disinfected the bed interior. For chloropicrin injection into polyethylene-mulched beds, 90-cm-wide beds were found to be more effective than the commonly used 60-cm-wide beds. Since the 90-cm-wide beds represented wider disinfested area than that by the 60-cm-wide beds, the author concluded that the control efficacy was high, but the treatments did not completely control the occurrence of sudden wilt. Combining the treatments with the use of the resistant rootstock C. ficifolia reliably decreased the incidence of sudden wilt, resulting in a 100% reduction in the three experiments compared to the untreated plots. The efficacy of each control measure varied, and thus, integrated methods are considered effective.
 The combination of the chloropicrin fumigation, polyethylene-mulched beds, and root restriction treatments was also effective because plant roots could grow in sterilized soil with root restriction treatments. However, the combination resulted in yield losses, because root restriction treatments induced stress in the cucumber plants. Therefore, improvement on the practical use of this combination is necessary.
 Soil fumigation by using chloropicrin (298.5 L a.i./ha) in deeper soil layers (approximately 30-cm depth) resulted in the adequate control of cucumber black root rot. In general, chloropicrin is directly introduced to the soil (at a 15-cm depth) and then covered with a plastic film to suppress its volatilization. In contrast, the chloropicrin deep-injection method is a very simple task, involving only soil surface compaction with a roller to seal off the air spaces between soil particles. Thus, this technique could also be regarded as labor-effective. However, this approach requires its registration as a new agricultural chemical (application expansion) because it is different from the currently used chloropicrin applications in Japan.

4. Control of cucumber black root rot through soil pH amendments by using a converter slag
 The results of seedling experiments and greenhouse tests showed that the converter slag (product name: Tenro Sekkai, a soil acidity amelioration material, which is a by-product of steelmaking) treatment of infested soil could prevent cucumber black root rot. Furthermore, this approach could significantly reduce the severity of disease while keeping soil pH levels high enough. However, physiological disorders were observed after this treatment in high-pH level soil (pH above 8.0; Haplic Andosols). The results suggest that the application of the converter slag to infested fields and maintenance of the soil pH at around 7.5 was optimal for the control of cucumber black root rot. The cucumbers grafted on pumpkin rootstock showed remarkable black root rot control after converter slag treatment, although sufficient effect was not seen in non-grafted cucumbers.
 Commercial field tests using cucumbers grafted on bloomless-type rootstock (Cucurbita moschata) showed that the technique could significantly reduce the severity of disease at a soil pH of 7.5 and a 10-cm amended soil depth (19,600 to 38,000 kg/ha, pH 7.5). No physiological disorders were observed in the cucumbers collected from six field tests that were conducted between 2009 and 2011. For this approach, a soil depth of 10cm is recommended based on the cost of the treatment and its control-effectiveness.
 In the next section, the factors responsible for disease suppression, calcium dosage, and soil pH elevation are described. The addition of CaSO
4 (soil pH did not change) to infested soil did not generate the same effect on seedling survival as that seen with CaCO3 or the converter slag (containing approximately 41.4% CaO) approaches. The results suggest that the elevation of soil pH, and not calcium supplementation of the soil, was responsible for disease suppression.
Estimation of genetic parameters for carcass traits and fatty acid composition in Japanese Black and Japanese Shorthorn of Iwate Prefecture
Youichi SATO, Junpei YASUDA, Chiemi YONEZAWA, Kazuya FUJIMURA and Mitsuhiro KUMAGAI
 Recently, the fatty acid composition of beef has attracted attention as a new trait that can affect taste. In order to achieve an improvement in both carcass traits and fatty acid composition, it is necessary to estimate genetic parameters in the target population and clarify the genetic association between carcass traits and fatty acid composition. In addition, there is little knowledge of the fatty acid composition of the Japanese Shorthorn. Therefore, our aim was to examine the improvement of fatty acid composition in a population of Japanese Shorthorn and Japanese Black Cattle in Iwate Prefecture by estimating the genetic parameters of carcass traits and fatty acid composition. We used 280 heads of Japanese Shorthorn and 1,050 heads of Japanese Black Cattle. With the program MTDFREML, we estimated the genetic parameters of fatty acid compositions CW, LMA, RT, SFT, BMS, C14:0, C14:1, C16:0, C16:1, C18:0, C18:1, C18:2, SFA and MUFA, and of carcass traits CW, LMA, RT, SFT, BMS. In addition, a relationship between genotypes SCD, FASN, and the MUFA breeding value of Japanese Black Cattle bulls was deliberated upon analysis. The heritability of fatty acid composition in Japanese Black cattle is lower than C18:2 at 0.19 but SFA and MUFA were as high as 0.81 and 0.79 respectively. In Japanese Shorthorn, we had estimated a moderate rate of heritability of fatty acid composition, but the difference in heritability of fatty acids was smaller than the Japanese Black Cattle. Genetic correlation and phenotypic correlation between the fatty acid ratio and carcass traits were found to be generally low in both cultivars. However, a moderate genetic correlation was estimated between the LMA and MUFA in Japanese Black Cattle, and between the MUFA and CW in Japanese Shorthorn. Effects of the SCD genotype were observed in the MUFA breeding value of Japanese Black Cattle bulls, and the difference between the V/V type and the A/A type was significant. The large fatty acid ratio in the Japanese Shorthorn population and the Japanese Black cattle population of Iwate Prefecture was found to greatly depend on genetics, and it was revealed that an improvement in genetics will be effective for improvement of fatty acid composition. Moreover, an association was observed between the SCD genotype and the MUFA breeding value of Japanese Black bulls. It should be noted that all known genes, including the SCD gene, merely describes a part of possible genetic capacity. However, it is possible to estimate the capability of SCD genotypes when breeding values cannot be estimated in a way we consider to be valid. It is believed that by watching research trends in the evaluation of eating quality of Japanese beef, and improving carcass traits, we can address the improvement of fatty acid composition, which will lead to improvements of taste and the future brand development of "Iwate Gyu."
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