Root Rot Resistance Research Articles

Status of resistance to Ascochyta blight and Fusarium wilt in large-seeded kabuli

Of the 390 Kabuli chickpea genotypes evaluated from 2005 to 2010 against Ascochyta blight (AB), Fusarium wilt (FW) and Dry root rot (DRR) resistance using standard screening techniques, 48 were found to be resistant to FW and DRR. Of these, four genotypes viz GLK95091, GLK95061, GLK24092 and GLK24096 showed resistance to AB with disease score less than 4.0 while another four genotypes GLK22072, GLK22098 and GLK24099 displayed AB disease score 5.0. GLK 22117 with FW percentage 6.3 and DRR 3.5 tested for seven years displayed good performance at other locations in India as well. Extra bold seeded genotypes GLK 26171, GLK26177 and GLK23001have shown good level of resistance to AB, FW and DRR and can be suggested as donors in crossing programme. It was observed that level of FW resistance was comparatively low in large-seeded and extra-large-seeded kabuli than small seeded kabuli.

Advances and perspectives on the gene mapping of root rot resistance in common beans

Common bean was originated in Mexico, and it is the most important protein source for millions of Mexicans, mainly those with low economic incomes. Grain yield of this crop is mainly affected by several fungal, bacterial and viral diseases. Among them, there are root rot diseases caused by the genera Macrophomina and Fusarium sp. Currently, some molecular biology tools such as DNA molecular markers are being used successfully to develop genetic maps where QTLs and major molecular markers are located, which are linked to genes that confer resistance to these fungi. The impor - tance of the development of genetic maps is based on the fact that they are the previous step for Marker-Assisted Selection (MAS). In this paper we review the current overview about the studies of root rot diseases mapping of resistance genes in common beans caused by the fungi M. phaseolina and Fusarium sp. We also report on those successful cases where results are translated to future applications in MAS in order to increase the efficiency of common bean breeding to both fungi based on costs, working and effectiveness. Finally, we analyze the perspectives of biotechnological tools on common bean breeding with special emphasis in Mexico.

Inheritance of Resistance to Phytophthora Root Rot in Chili Pepper Depending on Inoculum Density and Parental Genotypes

Phytophthora capsici Leonian causes root rot and stem blight in pepper (Capsicum spp.) and is a serious threat to pepper production because of its ability to infect every root, stem, and leaf at any developmental stage. Recently, pepper F1 cultivars resistant to Phytophthora root rot have been commercially released in Korea. However, despite many studies, the inheritance of resistance remains controversial due to differences in experimental methods, including pepper materials, pathogen isolates, inoculation conditions, and evaluation methods. Our aim was to determine the inheritance of Phytophthora root rot resistance by using three different F2 populations derived from crosses between ‘CM334’ (a resistant male parent) and three Korean landraces, ‘Subicho’ ‘Daehwacho’ and ‘Chilsungcho’ (susceptible female parents), and inoculating them with three different pathogen densities (1 ¯ 10 4 , 1 ¯ 105 , and 1 ¯ 106 zoospores/ml). The distribution patterns were varied, depending upon female parental susceptibility as well as inoculum densities. For example, as the inoculum density increased, pepper survival rates decreased. In all of the inheritance analyses, one common dominant resistant gene was participated in resistance to Phytophthora root rot. In addition, we found that a complementary gene, together with the major dominant gene, was necessary for resistance at a high (10 6 ) inoculum density, based on a 9:7 (R:S) segregation ratio. This study will be helpful in developing molecular markers linked to genes that are resistant to Phytophthora root rot.

Identification and development of molecular markers linked to Phytophthora root rot resistance in pepper (Capsicum annuum L.)

Phytopthora root rot in pepper (C. annuum) is caused by Phytophthora capsici L., which exhibits a high level of pathogenic diversity. Resistance to this disease is conditioned by a number of quantitative trait loci. Pyramiding resistance alleles is desirable and could be simplified by the use of molecular markers tightly linked to the resistance genes. The purpose of this study was development of molecular markers linked to Phytophthora root rot resistance. An F8 recombinant inbred line (RIL) population derived from a cross between YCM334 and a susceptible cultivar ‘Tean’ was used in combination with bulk segregant analysis utilizing RAPD and conversion of AFLP markers linked to Phytophtora root rot resistance into sequence-characterized amplified region (SCAR) markers. In conversion: one marker was successfully converted into a co-dominant SCAR marker SA133_4 linked to the trait. In bulked segregant analysis (BSA): three RAPD primers (UBC484, 504, and 553) produced polymorphisms between DNA pools among 400 primers screened. Genetic linkage analysis showed that the SCAR and RAPD markers were located on chromosome 5 of pepper. Quantitative trait locus (QTL) analysis showed that the SA133_4 and UBC553 were linked to Phytophtora root rot resistance. These markers were correctly identified as resistant or susceptible in nine promising commercial pepper varieties. These markers will be beneficial for marker-assisted selection in pepper breeding.

English

The incidence of root rot diseases partly contribute to the currently observed low percentage increase in the yield of cassava. We estimated gene diversities and identified putative hybridizing parents for root rot resistance using 18 simple sequence repeats loci in 43 improved genotypes of cassava. Root rot was measured over 2 years as the percentage proportion of rotten roots to the total number of roots harvested at 12 month after planting. Estimated rot ranged from 1.2 to 21.2% with a mean of 5.7±0.5. Rank-sum analysis generated 8 rot classes and identified TMS 96/1089A as best genotype resistant to root rot. Gene diversity analysis revealed expected heterozygosity that ranged from 0.701 for very highly susceptible genotypes to 0.781 for moderately resistant and susceptible. Genetic differentiation ranged from -0.0178 (resistant and susceptible) to 0.0523 (very highly resistant and highly resistant genotypes). A total heterozygosity of 0.764 was estimated and was largely due to within class diversity (0.755). DNA analysis representatives for window (DARwin) identified 10 hybridizing groups with a dissimilarity coefficient that ranged from 0.18 to 0.81 on a mean of 0.60. The results obtained from the present study are useful for the genetic improvement of cassava against root rot disease. Key words: Cassava genotypes, gene diversity, heterozygosity, resistant genotypes, root rot disease.

ROOT TRAITS ASSOCIATED WITH PHYTOPHTHORA ROOT ROT RESISTANCE IN RED RASPBERRY

ROOT TRAITS ASSOCIATED WITH PHYTOPHTHORA ROOT ROT RESISTANCE IN RED RASPBERRY

Evaluation of phytophthora root rot-resistant <i>Capsicum annuum</i> accessions for resistance to phytophthora foliar blight and phytophthora stem blight

A mixture of six Georgia isolates of Phytophthora capsici (Leon.), the causal agent of phytophthora blight, were used for greenhouse mass screening of over 700 accessions of Capsicum annuum for both stem blight and foliar blight. From this screening, it was determined that resistance to both forms of the disease were relatively common in the germplasm, but resistance to one form of the disease was not strongly correlated to resistance to the other form. Ten accessions previously shown to possess root rot resistance were tested for resistance to stem rot and leaf blight, and were found to also be highly resistant to these forms of the disease. It appears that single accessions have resistance to foliar, stem and root rot caused by P. capsici, which may simplify breeding for resistance to all three forms of the disease.

English

  Fusarium crown and root rot of tomato (Solanum lycopersicum) is the disease caused by the fungal pathogen Fusarium oxysporum f.sp. radicis-lycopersici(FORL). The most effective way to control this disease is to plant resistant varieties. Markers tightly linked to Fusarium crown and root rot could be used in breeding programs to introgress crown rot resistance into new varieties. In this study, we converted the random amplified polymorphic DNA (RAPD) marker UBC#116, linked to the Fusarium crown and root rot resistance gene (Frl), into a co-dominant sequence characterized amplified region (SCAR) marker. A fragment of about 480 bp, linked to the Frl gene, was polymerase chain reaction (PCR) amplified with the use of the UBC#116 primers, cloned and sequenced. A pair of primers were designed and PCR amplification was performed to develop a new SCAR marker for the Frl gene. The new marker was applied for the analysis of 96 tomato genotypes. The RAPD marker UBC#116 was also used and it revealed that the markers were equivalent to each other. However, the development of the new co-dominant SCAR marker has made marker-assisted selection (MAS) more practical, rapid and efficient.   Key words: Fusarium oxysporum f. sp. radicis-lycopersicum (FORL), marker-assisted selection (MAS), Solanum lycopersicum, breeding.

Genotypic and Phenotypic Variation among Pepper Accessions Resistant to Phytophthora capsici

Developing high levels of resistance to Phytophthora blight (Phytophthora capsici Leonian) of pepper (Capsicum annuum L.) is a goal of many pepper breeding programs. Genetic diversity and plant characteristics were evaluated on 21 pepper accessions previously identified as having high levels of Phytophthora root rot resistance. Accessions were evaluated for plant height, fruit size and shape, pericarp thickness, and pungency. Accessions varied widely from very unadapted material to those with more obvious breeding potential. Genetic diversity among the accessions was estimated using 22 simple sequence repeat (SSR) loci. Phytophthora capsici resistant accessions were identified that were not closely related to previously described sources of resistance. This information will allow breeders and researchers to further identify and incorporate novel sources of resistance to P. capsici into breeding programs. Accessions PI 201237 and PI 640532 appear to have the most potential for introgressing P. capcisi resistance into bell pepper.

Identification of isolate‐specific resistance QTLs to phytophthora root rot using an intraspecific recombinant inbred line population of pepper (Capsicum annuum)

Quantitative trait loci (QTL) for resistance to phytophthora root rot caused by Phytophthora capsici were investigated using two Korean P. capsici isolates and 126 F8 recombinant inbred lines derived from a cross of Capsicum annuum line YCM334 (resistant parent) and local cv. Tean (susceptible parent). The experimental design was a split plot with two replications. Highly significant effects of pathogen isolate, plant genotype, and genotype × isolate were detected. QTL mapping was performed using a genetic linkage map covering 1486·6 cM of the pepper genome, and consisted of 249 markers including 136 AFLPs (Amplified Fragment Length Polymorphisms), 112 SSRs (Simple Sequence Repeats) and one CAPS (Cleaved Amplified Polymorphic Sequence). Fifteen QTLs were detected on chromosomes 5 (P5), 10 (P10), 11 (P11), Pb and Pc using two data processing methods: percentage of wilted plants (PWP) and relative area under the disease progress curves (RAUDPC). The phenotypic variation explained by each QTL (R2) ranged from 6·0% to 48·2%. Seven QTLs were common to resistance for the two isolates on chromosome 5 (P5); six were isolate‐specific for isolate 09‐051 on chromosomes 10 (P10) and Pc, and two for isolate 07‐127 on chromosomes 11 (P11) and Pb. The QTLs in common with the major effect on the resistance for two isolates explained 20·0–48·2% of phenotypic variation. The isolate‐specific QTLs explained 6·0–17·4% of phenotypic variation. The result confirms a gene‐for‐gene relationship between C. annuum and P. capsici for root rot resistance.

Differential Gene and Protein Expression in Soybean at Early Stages of Incompatible Interaction with Phytophthora sojae

Soybean root and stem rot caused by Phytophthora sojae is a destructive disease worldwide. Using genetic resistance is an important and major component in the integrated pest management of this disease. To understand molecular mechanisms of root and stem rot resistance in soybeans, the gene and protein expression in hypocotyls and stems of variety Suinong 10 carrying resistance genes Rps1a and Rps2 was investigated by using mRNA differential display reverse transcription PCR and two-dimensional electrophoresis at 0, 0.5, 1, 2, and 4 h after inoculation with P. sojae race 1. The results of the comparison of gene and protein expression showed that at least eight differential fragments at the transcriptional level were related to metabolic pathway, phytoalexin, and signal transduction in defense responses. Sequence analyses indicated that these fragments represented cinnamic acid 4-hydroxylase gene, ATP β gene coding ATP synthase β subunit and ubiquitin-conjugating enzyme gene which upregulated at 0.5 h post inoculation, blue copper protein gene and UDP-N-acetyl-α-D-galactosamine gene which upregulated at 2 h post inoculation, TGA-type basic leucine zipper protein TGA1.1 gene, cyclophilin gene, and 14-3-3 protein gene which upregulated at 4 h post inoculation. Three resistance-related proteins, α-subunit and β-subunit of ATP synthase, and cytochrome P450-like protein, were upregulated at 2 h post inoculation. The results suggested that resistance-related multiple proteins and genes were expressed in the recognition between soybean and P. sojae during zoospore germination, penetration and mycelium growth of P. sojae in soybean.

Towards an understanding of the nature of resistance to Phytophthora root rot in red raspberry

A mapping population segregating for root rot resistance was screened under both field and glasshouse conditions over a number of seasons. Few correlations between field and glasshouse scores were significant. Final root rot scores were significantly negatively correlated with measures of root vigour. Two QTL associated with resistance were identified as were overlapping QTL for root vigour assessments. Markers significantly associated with the traits were used to identify BAC clones, which were subsequently sequenced to examine gene content. A number of genes were identified including those associated with stem cell identity, cell proliferation and elongation in the root zone, control of meristematic activity and organisation, cell signalling, stress response, sugar sensing and control of gene expression as well as a range of transcription factors including those known to be associated with defence. For marker-assisted breeding, the SSR marker Rub118b 110bp allele from Latham was found in resistant germplasm but was not found in any of the susceptible germplasm tested.

New consistent QTL in pea associated with partial resistance to Aphanomyces euteiches in multiple French and American environments.

Partial resistances, often controlled by quantitative trait loci (QTL), are considered to be more durable than monogenic resistances. Therefore, a precursor to developing efficient breeding programs for polygenic resistance to pathogens should be a greater understanding of genetic diversity and stability of resistance QTL in plants. In this study, we deciphered the diversity and stability of resistance QTL to Aphanomyces euteiches in pea towards pathogen variability, environments and scoring criteria, from two new sources of partial resistance (PI180693 and 552), effective in French and USA infested fields. Two mapping populations of 178 recombinant inbred lines each, derived from crosses between 552 or PI 180693 (partially resistant) and Baccara (susceptible), were used to identify QTL for Aphanomyces root rot resistance in controlled and in multiple French and USA field conditions using several resistance criteria. We identified a total of 135 additive-effect QTL corresponding to 23 genomic regions and 13 significant epistatic interactions associated with partial resistance to A.euteiches in pea. Among the 23 additive-effect genomic regions identified, five were consistently detected, and showed highly stable effects towards A.euteiches strains, environments, resistance criteria, condition tests and RIL populations studied. These results confirm the complexity of inheritance of partial resistance to A.euteiches in pea and provide good bases for the choice of consistent QTL to use in marker-assisted selection schemes to increase current levels of resistance to A.euteiches in pea breeding programs.

Introgression of Pythium root rot resistance gene into Rwandan susceptible common bean cultivars

A breeding scheme was carried out to introgress resistance genes to bean Pythiumroot rot in various commercial varieties grown in Rwanda. The achieved crosses were performed between three selected susceptible varieties (R617-97A, RWR 1668 and Urugezi) which are adapted to the various ecological production zones of Rwanda and two known sources of resistance to Pythium root rot(RWR719 and AND 1062). Following each inter varietal hybridization generation, a series of 4 successive back-crosses was achieved by using the susceptible parents as the initial parent lines to be improved for their respective behavior to Pythium root rot disease. At each back-cross generation, the PYAA 19800 SCAR marker linked toPythium root rot resistance in the two sources of resistance (varieties RWR 719 and AND 1062) was used to identify and to proceed to early selection of progenies possessing the gene of interest. The target materials serving for the molecular analyses were prepared from young trifoliate leaves of 2-weeks bean plantlets. It was observed that at each back-cross generation, there were variable proportions of plants exhibiting presence of the resistance gene according to the SCAR marker profiles. In addition to that observation mainly based to molecular profile, it was also revealed that the proportion of bean seeds having the same color as the susceptible parent line was increasing progressively. Finally, to assess if the individual plants exhibiting the SCAR marker are effectively resistant to the Pythium root rot disease, inoculation tests were carried out with a Pythium ultimum strain on each of them. This ultimate biological evaluation revealed that all the plants showing the SCAR marker were resistant to development of Pythium root rot symptoms after inoculation, confirming thus real introgression of the resistance characteristics through the breeding scheme adopted in our work. Key words: Phaseolus, vulgaris, Pythium, molecular, root rot, bean, genotype, resistance.

Selection of arbuscular mycorrhizal fungi for citrus growth promotion and Phytophthora suppression

In order to reduce unnecessary amount of P-fertilizer and severity of Phytophthora root rot in citrus orchards, the experiment was set up. Thirteen indigenous arbuscular mycorrhiza (AM) fungi species were isolated from rhizosphere soil of citrus orchards in Thailand and were then propagated into three host plants [sorghum ( Sorghum bicolor), maize ( Zea mays), and leek ( Allium cepa)] by trap culture. We also tested whether indigenous AMF species (13 different species) could colonize into three cultivars of citrus scions and rootstocks (Shogun: Citrus reticulata Blanco cv. Shogun; Tangerine: C. reticulata; and C-35 citrange: Citrus sinensis × Poncirus trifoliata). With root colonization rates, the results indicated that Acaulospora tuberculata and Glomus etunicatum provided the best colonization in all citrus cultivars. We selected, therefore, those AMF species to verify their influences on citrus growth and Phytophthora root rot resistance. Three cultivars of citrus scions and rootstocks, Shogun, Tangerine and C-35 citrange, were inoculated with two effective indigenous AMF species, G. etunicatum or A. tuberculata in order to determine the influences on citrus growth. The plants were investigated to determine the mycorrhizal efficiency index (MEI), AM colonization, P content, and other parameters. Co-inoculation of AMF species ( G. etunicatum or A. tuberculata) with Phytophthora nicotianae was also carried out in Shogun scion/C-35 citrange rootstocks. The results of citrus growth revealed that Shogun and Tangerine inoculated with G. etunicatum produced the highest MEI. Tangerine and C-35 citrange amended with fertilizers and G. etunicatum showed the highest P content in leaves. This indicated that G. etunicatum has an influence on citrus growth and P uptake, suggesting it to be the highly effective strain. Shogun scion/C-35 citrange rootstock combinations that were inoculated by both P. nicotianae and different AM fungi ( G. etunicatum or A. tuberculata) showed root injury at low level of root rot symptom. However, the part of Shogun scions grafted on rootstocks showed severe symptom of shoot die back in treatment inoculated with P. nicotianae alone, while treatment inoculated with different AM species ( G. etunicatum or A. tuberculata) and P. nicotianae rendered lower shoot die back symptoms than that of Phytophthora treatment. The low level of shoot die back symptom was shown at first, then healthy young shoot was restored. Our results indicated the facts that different host plants and different AMF species produced different outcomes of growth and pathogen resistance. The application of both AM isolates, therefore, has an enormous potential to be produced the inoculum for citrus orchards.

Growth, development and chemical characteristics of tobacco lines carrying black root rot resistance derived from Nicotiana glauca (Grah.)

With 1 figure and 4 tables AbstractFertile sesquidiploid BC1 of interspecific hybrids between N. tabacum cv. ‘Wiślica’ and N. glauca were previously produced to transfer N. glauca‐type resistance into tobacco. Tobacco breeding lines (‘WGL’) BC2F5–BC2F7 carrying black root rot resistance were obtained after one generation of backcrossing to cv. ‘Wiślica’ followed by five to seven generations of selfpollination. A 3‐year study was conducted to compare the agronomic value of ‘WGL’ lines with that of the parental cultivar ‘Wiślica’. Plant height and number of leaves per plant in all ‘WGL’ lines were similar to that of ‘Wiślica’. There were some significant variations for leaf characteristics. The most distinct effect was extended duration of the vegetative stage. All the ‘WGL’ lines showed delayed flowering compared to ‘Wiślica’. The ‘WGL’ lines were inferior to the parental cultivar with regard to weight of 10 dm2 of leaf blade. There were no major differences for nitrogen, sugars and nicotine contents. These results indicate that incorporation of the N. glauca‐type resistance into tobacco genome did not produce negative effects on morphological and chemical traits.

Identification of microsatellite markers linked to quantitative trait loci controlling resistance to Fusarium root rot in field pea

Feng, J., Hwang, R., Chang, K. F., Conner, R. L., Hwang, S. F., Strelkov, S. E., Gossen, B. D., McLaren, D. L. and Xue, A. G. 2011. Identification of microsatellite markers linked to quantitative trait loci controlling resistance to Fusarium root rot in field pea. Can. J. Plant Sci. 91: 199–204. Fusarium root rot, caused by Fusarium solani (Mart.) Sacc. f. sp. pisi (F. R. Jones) W. C. Snyder & H. N. Hans, is the most common root disease of field pea (Pisum sativum L.) in western Canada. In this study, a recombinant inbred line (RIL) population (n=71) of field pea, derived from crosses between a resistant cultivar Carman, and a susceptible cultivar Reward, was evaluated to identify quantitative trait loci (QTL) controlling resistance to Fusarium root rot. The parental genotypes and RILs were evaluated for resistance to root rot following inoculation with F. solani in field experiments during 2007 and 2008. The frequency distribution of disease severities among the RILs was continuous. Transgressive segregation for resistance was observed among the RILs, with five lines more resistant than Carman, but no lines were more susceptible than Reward. To identify DNA markers linked with the resistance, 213 microsatellite markers were screened with genomic DNA from the two parental cultivars. Only 14 markers were polymorphic between the two parents and were used to genotype each of the RILs. Quantitative trait loci analysis based on the mean disease severity data from 2007 and 2008 identified a QTL that explained 39.0% of the phenotypic variance in the RIL population. This QTL is flanked by markers AA416 and AB60 on linkage group VII. The microsatellite markers that are closely linked to this QTL may be useful for marker assisted selection to develop cultivars with superior Fusarium root rot resistance.

The Composition and Origins of Genomic Variation among Individuals of the Soybean Reference Cultivar Williams 82

Soybean (Glycine max) is a self-pollinating species that has relatively low nucleotide polymorphism rates compared with other crop species. Despite the low rate of nucleotide polymorphisms, a wide range of heritable phenotypic variation exists. There is even evidence for heritable phenotypic variation among individuals within some cultivars. Williams 82, the soybean cultivar used to produce the reference genome sequence, was derived from backcrossing a Phytophthora root rot resistance locus from the donor parent Kingwa into the recurrent parent Williams. To explore the genetic basis of intracultivar variation, we investigated the nucleotide, structural, and gene content variation of different Williams 82 individuals. Williams 82 individuals exhibited variation in the number and size of introgressed Kingwa loci. In these regions of genomic heterogeneity, the reference Williams 82 genome sequence consists of a mosaic of Williams and Kingwa haplotypes. Genomic structural variation between Williams and Kingwa was maintained between the Williams 82 individuals within the regions of heterogeneity. Additionally, the regions of heterogeneity exhibited gene content differences between Williams 82 individuals. These findings show that genetic heterogeneity in Williams 82 primarily originated from the differential segregation of polymorphic chromosomal regions following the backcross and single-seed descent generations of the breeding process. We conclude that soybean haplotypes can possess a high rate of structural and gene content variation, and the impact of intracultivar genetic heterogeneity may be significant. This detailed characterization will be useful for interpreting soybean genomic data sets and highlights important considerations for research communities that are developing or utilizing a reference genome sequence.

Resistance of Pepper to Phytophthora Crown, Root, and Fruit Rot Is Affected by Isolate Virulence.

Greenhouse and laboratory experiments were conducted to determine the virulence of four Phytophthora capsici isolates from Michigan to 31 bell and hot pepper cultivars and breeding lines. Resistance to crown and root rot was assessed following the inoculation of soilless media with P. capsici-infested millet seed. In a detached fruit assay, fruit rot resistance was evaluated following inoculation with zoospore suspensions of 1.75 × 106 zoospores/ml. The four isolates differed in virulence to pepper lines screened for crown and root rot resistance and were considered to be four different physiological races. The pepper lines CM334, NY07-8001, NY07-8006, and NY07-8007 were resistant to the isolates tested. None of the commercial cultivars were resistant to P. capsici isolate 12889, but several cultivars were resistant to the other isolates screened. The isolates varied in their ability to cause infection on the fruits of the different cultivars. Overall, pepper fruit were more susceptible to P. capsici than the roots and crowns. Management of Phytophthora crown and root rot of pepper can be improved through the use of resistant cultivars. However, since isolate virulence affects resistance, cultivar resistance will need to be utilized on a local scale accordingly.

Genomic regions associated with common root rot resistance in the barley variety Delta

Common root rot (CRR) caused by Bipolaris sorokiniana is a serious disease constraint in the dry temperate cereal growing regions of the world. Currently little is known about the genetic control of resistance to CRR in cereals. In this study based on a Delta/Lindwall barley population we have undertaken a bulked segregant analysis (BSA) and whole genome mapping approach utilising Diversity Arrays Technology (DArT) to identified quantitative trait loci (QTL) associated with CRR expression. One QTL each was identified on chromosomes 4HL and 5HL explaining 12 and 11% of the phenotypic variance, respectively.