Inheritance of resistance to Striga gesnerioides biotypes from Mali and Niger in cowpea (Vigna unguiculata (L.) Walp.)

Pot and laboratory experiments were performed in order to elucidate the genetics of resistance of three cowpea (Vigna unguiculata (L.) Walp.) resistant sources to two biotypes of the parasitic weed Striga gesnerioides (Willd.) Vatke (witchweed). B301, Suvita-2 and IT82D-849 were crossed to susceptible cultivars. Roots of each plant of parental, F₁, F₂, BC₁ and BC₂ populations were washed free of soil and examined closely for S. gesnerioides attachment. Data on resistant and susceptible cowpea plants were analyzed using the chi-square test to ascertain the goodness of fit to different genetic ratios. Segregation patterns indicate monogenic dominant inheritance of resistance to both S. gesnerioides biotypes in B301. Suvita-2, which is susceptible to the biotype from Maradi, Niger, showed segregation patterns that indicate monogenic dominant inheritance of resistance to S. gesnerioides biotype from Cinzana, Mali. Results also indicate monogenic dominant inheritance of resistance to S. gesnerioides biotype from Cinzana in IT82D-849. However, the inheritance of resistance to the biotype from Maradi would be monogenic and recessive in this line. These results suggest that the resistance of all three sources would be easy to transfer to promising breeding lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Virulence characteristics of a new race of the parasitic angiosperm,Striga gesnerioides,from southern Benin on cowpea (Vigna unguiculata)

An in vitro growth system was used to determine the virulence of two samples of Striga gesnerioides from Zakpota in southern Benin. Cowpea variety B301, previously considered resistant to all races of S. gesnerioides, was susceptible to both samples of the parasite. Two other cowpea varieties, 58–57 and IT81D-994, were totally resistant. Resistance in 58–57 was associated with a hypersensitive necrosis of infected roots, whilst IT81D-994 supported production of small S. gesnerioides tubercles with stems which failed to develop. Striga gesnerioides from southern Benin is the fourth race of the parasite to be identified, and the first with virulence on variety B301. The implications for breeding cowpeas with resistance to S. gesnerioides are discussed.Abbreviations IITA International Institute of Tropical Agriculture - LARS Long Ashton Research Station - SAFGRAD Semi-Arid Food Grain Research and Development     

Genetic inheritance of resistance to cowpea aphid-borne mosaic virus in cowpea

Cowpea aphid-borne mosaic virus (CABMV) is a major virus disease in Uganda that causes substantial loss of the cowpea crop especially in growth and yield. The mode of gene action conferring resistance to the virus is not well understood. The objective of the study was to determine the genetic inheritance of resistance in cowpea crosses. Three susceptible (S) cowpea landraces that are commonly grown by farmers were crossed with five introduced resistant cowpea varieties in accordance with a North Carolina mating design II scheme. The F₁, F₂ and BC₁F₁ progenies generated were evaluated in the field together with their parents. They were then infected with two infection methods namely: by spreader-rows of S cultivar (Ebelat) and artificial inoculation of virus extracts. The results obtained showed that general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive gene effects controlled virus infection. The results further demonstrated that the GCA effects (59.8?%) were more important than SCA effects (40.2?%) in determining virus resistance in the cowpea varieties. Utilisation of good general combiners of the varieties MU-93, IT82D-516-2, SECOW-2W and IT85F-2841 in hybridisation to improve virus resistance in cowpea crosses would be recommended. The result of this study provided an indication that CABMV resistance was conditioned by more than one recessive gene in eight populations, but also revealed resistance to be conditioned by a single recessive gene in the other seven populations. Observation of continuous distribution of progenies for severity data in the F₂ populations also confirmed significance of quantitative inheritance for CABMV resistance. Therefore, the significance of GCA effects suggests that recurrent selection could be applied to accumulate the additive genes for resistance in F₂ populations.     

Resistance of cowpea and cereals to the parasitic angiospermStriga

Summary Striga species are parasitic angiosperms that attack many crops grown by subsistence farmers in sub-Saharan Africa and India. Control of the parasite is difficult and genetically resistant crops are the most feasible and appropriate solution. In cowpea, complete resistance toStriga gesnerioides has been identified. Breeding for resistance in sorghum has identified varieties with good resistance toS. asiatica in Africa and India. One variety was also resistant toS. hermonthica in W. Africa. No such resistance toStriga has been found in maize or millets.Resistant varieties have usually been sought by screening germplasm in fields naturally infested withStriga. However, laboratory techniques have also been developed, including anin vitro growth system used to screen cowpeas for resistance toS. gesnerioides. Two new sources of resistance in cowpea have been identified using the system. The technique has also been used to investigate the mechanisms of resistance in this crop. Two mechanisms have been characterised, both were expressed after penetration of cowpea roots by the parasite.The resistance of some sorghum varieties toStriga is controlled by recessive genes. In cowpea, resistance toStriga is controlled by single dominant genes. The genes for resistance are currently being transferred to cowpea varieties which are high yielding or adapted to local agronomic conditions. OneStriga resistant cowpea variety, Suvita-2, is already being grown widely by farmers in Mali. Reports of breakdown of resistance in cowpea toStriga have not yet been confirmed, but a wider genetic base to the resistance is essential to ensure durability ofStriga resistance.Abbreviations ICRISAT International Crops Research Institute for the Semi-Arid Tropics - IITA International Institute of Tropical Agriculture - LARS Long Ashton Research Station - SAFGRAD Semi-Arid Food Grain Research and Development     

Breeding cowpea for resistance to Striga gesnerioides in the Nigerian dry savannas using marker‐assisted selection

Historically, conventional breeding has been the primary strategy used to develop a number of Striga‐resistant varieties currently grown in the Sahel of Western Africa. In this study, we have successfully developed and applied a marker‐assisted selection strategy that employs a single backcross programme to introgress Striga resistance into farmer preferred varieties of cowpea for the Nigeria savannas. In this strategy, we have introduced the Striga resistance gene from the donor parent IT97K‐499‐35 into an elite farmer preferred cowpea cultivar ‘Borno Brown’. The selected 47 BC₁F₂ populations confirmed the recombinants with desirable progeny having Striga resistance gene(s). The 28 lines selected in the BC₁F_2:4 generation with large seed size, brown seed coat colour and carrying marker alleles were evaluated in the field for resistance to Striga resistance. This led to the selection of a number of desirable improved lines that were immune to Striga having local genetic background with higher yield than those of their parents and standard varieties.     

Genetic markers linked to Striga gesnerioides resistance for the improvement of Ghanaian cowpea (Vigna unguiculata) cultivars

The parasitic plant, Striga gesnerioides (Willd.) Vatke, is one of the most important constraints of cowpea production and food security in West Africa. Currently, few Striga resistant cowpea varieties have been developed that are well‐adapted to the dry savannah regions of Ghana. While genes conferring resistance to Striga races SG1, SG3 and SG5 have been mapped, the genetic locus of resistance to the race of Striga found in Ghana (SG‐GH) has not been characterized. Here, we report identification of genetic markers linked to SG‐GH resistance and define the relationship of this locus to SG3 resistance in recombinant inbred line populations generated from crosses between Striga resistant IT97K‐499‐35 and the Striga susceptible varieties Apagbaala and SARC‐LO2. The populations were genotyped with five genetic markers associated with SG3 and SG5 Striga resistance genes and a genetic map was developed. Genes conferring resistance to SG‐GH and SG3 mapped 4.2 cM from each other on chromosome Vu11. The identification of genetic markers linked to SG‐GH resistance will facilitate the marker‐assisted development of high‐quality Striga resistant cowpea varieties in Ghana.     

New sources of resistance of cowpea (Vigna unguiculata) toStriga gesnerioides,a parasitic angiosperm

Summary Thirty-seven accessions of cowpea and yard-long bean were assessed for resistance toStriga gesnerioides. Cowpea plants were grown using anin vitro method, then inoculated with young seedlings ofS. gesnerioides produced from seed from three West African countries. Resistance was assessed by comparing the number and size ofS. gesnerioides tubercles on these accessions with those on a known susceptible cowpea, cv. Blackeye. Two cowpea landraces, APL-1 and 87-2, were completely resistant toS. gesnerioides from Burkina Faso, Mali and Cameroon and partially resistant toS. gesnerioides from Niger. Complete resistance was expressed either as a hypersensitive response of infected root tissues or as a severely retarded development of successful infections. All other accessions, including three samples of yard-long bean were susceptible toS. gesnerioides. The original 87-2 plants segregated for resistance and susceptibility. However, uniformly resistant progeny were obtained by producing seed from vegetatively propagated clones of single resistant 87-2 plants. Resistance of APL-1 and 87-2 toS. gesnerioides was confirmed in pot and field trials. Neither of these cowpeas were resistant toAlectra vogelii. Varieties APL-1 and 87-2 provide additional sources of resistance to most races ofS. gesnerioides, including a newly discovered virulent race from Benin.Abbreviations ICRISAT International Crops Research Institute for the Semi-Arid Tropics - IITA International Institute of Tropical Agriculture - SAFGRAD Semi-Arid Food Grain Research and Development     

Quantitative resistance to Cercospora leaf spot disease caused by Pseudocercospora cruenta in cowpea

Six populations (Parent 1, Parent 2, F1, F2, BC1 and BC2) generated from each of four crosses involving four resistant and two susceptible varieties of cowpea (Vigna unguiculata L. Walp) were evaluated for resistance to Cercospora leaf spot (CLS) disease caused by Pseudocercospora cruenta under induced epiphytotic conditions, in four separate field experiments. Climatic conditions determined the onset of CLS disease in the susceptible cultivar and varied in the four experiments from 35 to 48 days after planting (DAP). Genetic analysis revealed that the mode of inheritance of resistance to P. cruenta can be oligogenic or polygenic depending upon the cross. This is the first report of polygenic inheritance of CLS resistance. Number of nodes infected fitted a simple additive dominance model with predominance of additive effects based on generation mean analysis. Oligogenic resistance was observed for the other three crosses, with the most plausible models being: a single gene model with incomplete dominance in CB27 × IT87D-939-1; a single gene model with complete dominance in CB27 × VRB-10; and a triger model in Los Banos Bush Sitao × IT86D-792, based on segregation analysis of symptomatic : non-symptomatic plants. The role of minor genes was also indicated in the above crosses. Suggested approaches to breeding for resistance to CLS are discussed.     

Combining ability analysis and association of yield and yield components among selected cowpea lines

The study was carried out to determine combining ability and association of yield and yield components among crosses derived from seven selected cowpea (Vigna unguiculata (L.) Walp) parents. Twenty-one hybrids were generated from diallel crosses excluding reciprocals. Hybrids along with seven parents were studied for combining ability and phenotypic correlations for seed yield and eight yield components. The result indicated that the general combining ability (gca) and specific combining ability (sca) were significant for most characters indicating the importance of both additive and non-additive genetic components. Additive gene action was important for eight characters except pod number, whereas non-additive gene action was not important for nodule number and grain yield. Parental lines IT86D-716 and IT81D-985 were found to be good general combiners for grain yield and other traits. The most promising specific combiners for yield and yield components were from crosses including IT87D-697-2 × IT86D-716, IT88D-867-11 × IT86D-716, IT93K-624 × IT87D-697-2, and IT87D-697-2 × IT92KD-405-1. Significant positive phenotypic correlations were observed between seed yield with pod length (POL), number of pods per plant (PON), and number of seeds per pod (SPD). POL, pod number per plant, SPD, and grain yield were identified as the best selection criteria that could be used in cowpea breeding programs.     

Identification of new sources of resistance to Striga gesnerioides in cowpea germplasm

There have been reports of breakdown of striga resistance in previously resistant cowpea cultivars in Burkina Faso. This could be attributed to new striga races emerging or to an increase in the aggressiveness of current striga races. Therefore, cowpea genotypes were evaluated in fields infested with S. gesnerioides at three striga hot spots in Burkina Faso and in pots under artificial infestation with striga races SR 1, SR 5 and SR Kp to identify new, adapted and striga‐resistant sources. Cowpea genotypes showed differential reactions for striga resistance over sites and for striga races in pot experiments, indicating differences in the races involved, and SR Kp was reported as a new race. Resistant sources conferring site‐specific or multiple striga‐race resistance were identified. Genotypes 58‐57, Sanga 2, IT84S‐2049, IT98K‐205‐8, IT93K‐693‐2, KVx771‐10, KVx775‐33‐2, KVx61‐1, Gorom local, Mouride and Melakh conferred resistance to all three striga races. These genotypes are potential donor parents for breeding new, adapted and striga‐resistant genotypes. Cowpea landraces including Moussa local and Niaogo local with farmers' preferred traits were susceptible and need improvement for striga resistance.     

Heritability and gene effects for incorporating pubescence into cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> (L) Walp.) from <Emphasis Type="Italic">V. rhomboidea</Emphasis> Burtt. Davy

Cowpea, an important subsistence pulse crop in the tropics and subtropics is susceptible to several insect pests that seriously limit its yield potential. Pubescence (hairiness) on the parts of some of its wild relatives has been reported to reduce the damage caused by some of the insect pests. A generation mean analysis was conducted between a cowpea variety IT82D-716 and two accessions of Vigna rhomboidea to investigate the gene effects and heritability for incorporating pubescence into cultivated cowpea from V. rhomboidea. The additive-dominance model that was adopted in the analysis was observed to sufficiently explain the mode of inheritance of leaf and stem pubescence with the additive effect being more important than the dominance effect. A six-parameter model with epistatic gene interactions was adequate for explaining the inheritance of pod pubescence. Heritability estimates, in the narrow sense were high for pubescence density and pubescence length. Inheritance of pubescence in crosses between cowpea and V. rhomboidea was governed by one and two genes. Significant and higher additive gene effects and high-heritability suggest that backcross selection schemes should be responsive in the development of pubescent cowpea lines.     

Response to Selection for Resistance to Macrophomina and Xanthomonas and its Association with Seed Colour in Cowpea*

In cowpea, black seeded types are supposedly resistant to Macrophomina. A study was undertaken to verify the association of seed colour with resistance to Macrophomina and Xanthomonas and to examine the response over three cycles of selection for such resistance along with seed yield, determinate habit and synchronous flowering in five black-and three white-seeded cowpea varieties. Selection was done between and within progenies under heavy natural incidence of both pathogens supplemented by artificial inoculation of Macrophomina using the toothpick method at flower primordial stage. Among 414 single plant progenies in the first cycle all 193 white-seeded progenies from three different varieties were highly susceptible to both pathogens, with considerable variation among the black-seeded ones. All the black- and white-seeded progenies derived from the same variety‘Floricream’were highly susceptible. Multivariate analysis for five characters in the ten best progenies after two selection cycles revealed significant genetic diversity between the progenies. Selection was successful with the isolation of three productive progenies resistant: to both diseases. The results indicated that seed colour had no influence on resistance m this material and that simultaneous improvement of seed yield, plant type and disease resistance could be achieved.     

陆稻抗旱性主要指标的研究

在大田栽培水分子缺条件下，对３个陆稻品种的部分抗旱指标进行了测定，分析在正常供水与水分胁迫两种条件下的生理反应差异，从而对其抗旱性鉴定进行了探讨。结果表明，水分胁迫下的叶片游离脯氮酸含量，可溶性糖含量，叶细胞膜透性，组织相对含水量，离体叶片失水百分率，根冠比等都可作为陆稻抗旱性鉴定指标，并应用以上指标采取模糊隶属法对３个品种的抗旱性进行了综合评价，合江５号属全期弱抗品种，东陆１号全期中抗品种，推广     

棉花黄萎病菌与品种互作的格局分析

 以23个棉花品种(系)接种18个黄萎病菌株的抗感表现(病情指数)为分析对象,在聚类分析的基础上用双标图方法研究了寄主 病原的互作格局。结果表明：23个棉花品种分为6个抗病性不同的品种组,18个菌株聚为5个致病力不同的菌株群。5031和50312组成的品种组G1对所有菌株群具有最高抗性,可作为抗黄育种的高抗质源。来自河北成安的VD25与来自江苏常熟的XS4、XS6和XS7组成的菌株群S4与G5品种组存在互作,其致病力最强,是棉花黄萎病的优势菌株群,在抗黄育种和抗黄鉴定中应予以高度重视。S2和S3菌株群与56%的参试品种构成的3个品种组间存在互作,是潜在的优势菌株群。具平均抗病性的G2品种组是黄萎病菌的优良寄主。     

Performance of cowpea varieties under <Emphasis Type="Italic">Striga gesnerioides</Emphasis> (Willd.) Vatke infestation using biplot analysis

Striga gesnerioides (Willd) Vatke, is a major destructive parasitic weed of cowpea (Vigna unguiculata (L.) Walp.) which causes substantial yield reduction in West and Central Africa. The presence of different virulent races within the parasite population contributes to significant genotype × environment interaction, and complicates breeding for durable resistance to Striga. A 3-year study was conducted at three locations in the dry savanna agro-ecology of Nigeria, where Striga gesnerioides is endemic. The primary objective of the study was to identify cowpea genotypes with high yield under Striga infestation and yield stability across test environments and to access suitability of the test environment. Data collected on grain yield and yield components were subjected to analysis of variance (ANOVA). Means from ANOVA were subjected to the genotype main effect plus genotype × environment (GGE) biplot analysis to examine the multi-environment trial data and rank genotypes according to the environments. Genotypes, environment, and genotypes × environment interaction mean squares were significant for grain yield and yield components, and number of emerged Striga plants. The environment accounted for 35.01%, whereas the genotype × environment interaction accounted for 9.10% of the variation in grain yield. The GGE biplot identified UAM09 1046-6-1 (V7), and UAM09 1046-6-2 (V8), as ideal genotypes suggesting that these genotypes performed relatively well in all study environments and could be regarded as adapted to a wide range of locations. Tilla was the most repeatable and ideal location for selecting widely adapted genotypes for resistance to S. gesnerioides.     

小麦品种的麦红吸浆虫抗性分级方法及抗性评价

为了简化小麦品种对麦红吸浆虫抗性的鉴定方法,评价我国冬小麦主栽品种对吸浆虫的抗感性,2008-2012年在河南洛阳田间,连续调查鉴定麦红吸浆虫对我国小麦主栽品种的虫穗率(ISP)与损失率,分析其相关性。结果表明ISP和损失率存在显著的相关性。在田间吸浆虫高密度下,ISP定级方法比相对定级方法更能表现品种的抗性和敏感程度,各抗级的指标依次为0 (免疫)、0 < ISP < 20 (高抗)、20 ≤ ISP < 40 (中抗)、40 ≤ ISP < 60 (中级)、60 ≤ ISP < 80 (感)和ISP ≥ 80 (高感)。我国冬小麦的主要生产品种对吸浆虫均为感虫或高感,而荆麦66表现为高抗,我国小麦中极度缺乏抗虫品种。鉴定结果表明,ISP定级方法简便高效,可以取代相对定级法用于小麦抗红吸浆虫的鉴定。     

Screening of Ethiopian sorghum (Sorghum bicolor) landraces for their performance under Striga hermonthica ‐infested conditions

Striga hermonthica is a major constraint to sorghum production and productivity in sub‐Saharan Africa, Ethiopia, in particular. The objectives of this study were to evaluate the performance of 49 sorghum genotypes based on their reaction to S. hermonthica and investigate the relationships among yield and Striga resistance traits, including the Striga emergence count, area under Striga number progress curve, area under Striga severity progress curve, grain yield under infested, grain yield under non‐infested conditions and relative yield loss. The genotypes differed significantly in all measured parameters under Striga‐infested and non‐infested conditions. The genotypes ‘Birhan’, ‘Gubiye’, Wolegie, Zegerie, Nechmashila I, Woftel, Tetron and Eyssa were identified as promising ones based on grain yield and Striga‐related traits. On the other hand, the genotypes Jamyo, Bobie, Gedido, Mankebar and Zengada had moderate Striga numbers with low relative yield loss as compared with susceptible checks. The most promising variety, Zegerie, Mankebar and Zengada, out yielded the standard resistant checks ‘Birhan’ and ‘Gubiye’ under Striga infestation. Ward cluster analysis grouped the 49 sorghum genotypes in to four distinct clusters under Striga‐infested conditions. All members of clusters II and III showed the highest yielding group with the lowest to moderate Striga number, while cluster IV supported the lowest yield with the highest Striga number. Significant negative correlations were observed between yield‐ and Striga‐related traits. Highly significant and strong correlations were observed among Striga resistance indices, indicating that any of the Striga resistance parameters can be used as an indicator of resistance. The wide variations in grain yield among genotypes under Striga‐infested conditions would be invaluable genetic resources for production in Striga endemic areas of Ethiopia.     

Isolation, sequence analysis, and linkage mapping of resistance-gene analogs in cowpea (Vigna unguiculata L. Walp.)

Degenerate oligonucleotides designed to recognize conserved coding regions within the nucleotide binding site (NBS) and hydrophobic region of known resistance (R)genes from various plant species were used to target PCR to amplify resistance gene analogs (RGAs) from a cowpea (Vigna unguiculata L. Walp.) cultivar resistant to Striga gesnerioides. PCR products consisted of a group of fragments approximately 500 bp in length that migrated as a single band during agarose gel electrophoresis. The nucleotide sequence of fifty different cloned fragments was determined and their predicted amino acid sequences compared to each other and to the amino acid sequence encoded by known resistance genes, and RGAs from other plant species. Cluster analysis identified five different classes of RGAs in cowpea. Gel blot analysis revealed that each class recognized a different subset of loci in the cowpea genome. Several of the RGAs were associated with restriction fragment length polymorphisms, which allowed them to be placed on the cowpea genomic map. The potential for using these sequences to isolate R genes, and subsequent direct manipulation of disease and pest resistance using genetic engineering is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

小麦新品种绵麦39成株期抗条锈性的遗传分析

绵麦39是绵阳市农业科学研究所育成的小麦新品种,2005年通过四川省品种审定后在大面积生产上推广应用,表现高抗条锈病且抗性稳定。为明确绵麦39抗条锈性遗传基础,本试验选用7个抗病品种（系）和3个感病品种（系）,分别与绵麦39组配成抗×抗、抗×感组合进行遗传分析。结果表明,绵麦39对条锈菌条中32的成株期抗性主要受一对显性基因的控制;绵麦39对条中32号的抗性来源于抗条锈病材料贵农21-1（含有条锈病抗性基因YrGn21）。抗性基因YrGn21与YrCH42、Yr26基因具有等位性关系,而与抗条锈病材料贵农19-4、辽春10号以及CIMMYT材料oxley、96EW39（SW2148）含有的条锈病抗性基因有差异。同时对各抗病品种（系）的抗条锈性进行了探讨。     

向日葵菌核病田间接种方法及品种抗病性研究

建立有效的向日葵菌核病盘腐田间接种鉴定方法,对向日葵抗性资源筛选和抗病育种具有重要意义。试验以菌核病菌PDA菌丝体悬浮液、高粱粒菌丝体和子囊孢子悬浮液作为接种物,分别对不同抗感向日葵品种在R5.1（始花期）、R5.5（半开花期）和R6（盛花期）进行人工接种,从而筛选出最佳接菌物类型、浓度及接种时期,并用此方法对18个品种连续2年进行了抗性评价。试验结果表明：3种接种物均可使不同向日葵抗感品种产生盘腐症状。PDA菌丝体为30.0 g/L、高梁粒菌丝体为0.4 g/盘和子囊孢子为1×10³个/mL浓度即可区分出向日葵品种间抗感性差异。R5.1~R5.5接种较R6可获得更高的发病率及病情指数。正交试验结果表明,田间盘腐接种的最佳条件为：接种物为子囊孢子悬浮液,浓度为1×10³个/mL,接种时期为R5.1,保湿时间为48 h。同时筛选出4个对盘腐型菌核病表现抗病的向日葵品种。本研究所建立的向日葵田间接种方法能够有效地对向日葵进行抗菌核病筛选和鉴定。