Resistance Breeding Programs Research Articles

Susceptibility of Flordaguard peach rootstock to a resistant-breaking population of Meloidogyne floridensis and two populations of Meloidogyne arenaria.

Cultivar Flordaguard is suggested as a root-knot nematode (RKN) resistant rootstock for Florida peaches, however, RKN disease has been observed on this rootstock in peach orchards. Our goal was to confirm whether the RKN resistance breaking isolates of M. floridensis and M. arenaria indeed could infect and reproduce on the peach rootstock cv. Flordaguard in both laboratory and field studies. Root galling occurred on all peach cultivars evaluated including Flordaguard, Flordaglo, Okinawa, and Lovell, in the presence of the RKN resistance-breaking isolates of M. floridensis (MfGnv14) and two M. arenaria isolates (Ma1 and Ma2). These rootstocks showed varying degrees of susceptibility (to a lesser extent in Okinawa) to these three RKN resistance-breaking isolates. The importance of nematode inoculum concentrations in differentiating between resistance and susceptible plants was demonstrated, and thus are an important factor to consider in nematode resistance breeding programs. In host differential tests the peach-originated isolates of M. floridensis and M. arenaria behaved similarly with the vegetable-originated isolates of M. floridensis on tomato, peanut, watermelon, and tobacco, but showed variable host responses on cotton and pepper. The two M. arenaria isolates from peach reproduced on pepper but not on peanut. To our knowledge this is the first report of M. arenaria race 3 infecting Flordaguard and pepper in Florida. Soil and root samples collected from cv. Flordaguard infected trees at two commercial peach orchards showed that M. floridensis and M. arenaria were established on the rootstock.

First Report of Peanut Stripe Virus Infecting Groundnut (<i>Arachis hypogaea</i> L.) in Western Kenya

Peanut (<i>Arachis hypogaea</i>) is a leguminous food crop in Kenya, whose yields are probably affected by Peanut stripe virus (PStV) belonging to the genus Potyvirus and family <i>Potyviridae,</i> that causes Peanut stripe disease (PSD), also referred to as groundnut stripe disease (GSD). PSD/GSD is rapidly spread through seed and mechanically transmitted in a non-persistent manner by aphid vectors causing 30-100% decrease in production. Different isolates of PStV induce different symptoms in groundnut ranging from striping, ring spots, vein banding and oakleaf mosaic. PStV occurrence in Kenya has neither been reported nor its resistance identified in commercial cultivars of groundnut in research stations. This informs the need for resistance breeding programmes of wild genotypes to be explored as the only practical solution. This study reports the first occurrence, distribution and molecular detection of PStV infecting groundnut in western Kenya, which is crucial in developing appropriate crop protection and plant health management strategies for this new disease. A survey of PSD was conducted in western Kenya among the four counties of Bungoma, Busia, Kisumu and Kisii during the short rains season of 2019. A total of 14 symptomatic leaf samples were selected from the collected samples and preserved until use. Total RNA was extracted from the symptomatic leaf samples using GeneJET Plant RNA Purification Mini Kit according to the manufacturers’ protocol. Two-step RT-PCR detection of PStV was done using specific primers that yielded the expected 454 bp. DNA libraries were prepared and sequenced using the Sanger sequencing platform, but produced poor quality sequences after performing sequence quality check using BioEdit workbench that based on the low quality peaks of the electropherograms generated, therefore recommend for further research. To our knowledge, this is the first report of the occurrence, distribution and molecular diagnostics of PStV in Kenya. Further studies are needed to assess the molecular and biological diversity of PStV strains, the spatial distribution and the incidence of this emerging groundnut disease in Kenya.

DNA Fingerprinting of Bruchid Resistant Mung Bean Genotypes Using SSR Markers

Genetic diversity analysis of bruchid resistant accessions helps in identifying efficient genetic stock for resistance breeding programs. Eighteen mung bean accessions having moderate to high levels of resistance were genetically differentiated using simple sequence repeat (SSR) markers. Eight SSRs marker (CEDG037, CEDG021, CEDG044, CEDG127, CEDG154, CEDG178, CEDG214 and CEDG305), were found polymorphic and thus useful for complete transferability of resistant QTL/genes to a susceptible variety. The maximum number of SSR bands was amplified by the primer CEDG-305. The PIC value of primers ranged from 0.32 to 0.49 with mean of 0.42. Resolving power ranged from 1.01- 1.36. The unweighted neighbour-joining (UNJ) dendrogram constructed on the basis of genetic similarity matrix grouped the 18 genotypes into two major clusters. Cluster I comprised of three genotypes such as KM-7-134, KM-11-32 and KM-12-5 and Cluster II comprised of remaining, further divided into Cluster II A (14 genotypes) and Cluster II B (M1319B). Mung bean accessions KM-11-10 and PS-16 can be considered for reducing the storage loss, as these were found relatively resistant.

Identification of novel sources for resistance against ascochyta blight and botrytis grey mould of chickpea

Ascochyta blight (Ab) and botrytis grey mould (bGM) are the major foliar diseases of chickpea that can cause severe yield losses. Thus, to identify stable sources, a set of 388 lines including 288 lines from Reference Set of chickpea and 100 advanced breeding lines were screened at PAU, Ludhiana for two years against Ab and bGM. One accession, ICC 1915, from the Reference Set and 24 advanced breeding lines were found resistant against Ab. None of the lines was found resistant against bGM, however, some lines were found moderately resistant. The identified lines can be used as sources of resistance in the disease resistance breeding programmes.

&lt;p&gt;&lt;strong&gt;Biochemical defense in maize against &lt;em&gt;Chilo partellus&lt;/em&gt; (Swinhoe) through activation of enzymatic and nonenzymatic antioxidants&lt;/strong&gt;&lt;/p&gt;

Biochemical defense against herbivores is one of the most important components of plant resistance to insects. Here, we studied the constitutive and induced biochemical defense through activation of enzymatic and nonenzymatic antioxidants in response to damage by the spotted stem borer, Chilo partellus (Swinhoe) in six maize genotypes including resistance and susceptible checks. The levels of total sugars, total soluble protein and starch were significantly lower, while total phenol and total antioxidant higher in resistant than susceptible maize genotypes both under damaged and healthy plant conditions. The activity of antioxidant enzymes like AO, CAT, APX, PAL and TAL were significantly higher in resistant than susceptible genotype, Basi Local, which further increased in response to damage by C. partellus . The nonenzymatic antioxidant scavenging activity of FRAP was also significantly higher in resistant maize genotypes, which further increased upon damage by C. partellus . Total antioxidant activity increased from 22.2 to 96.3% across test maize genotypes in response to damage by C. partellus , wherein maximum increase was recorded in CML 345. These findings clearly demonstrate that both constitutive and induced biochemical compounds through activation of enzymatic and nonenzymatic antioxidant defense systems impart resistance against C. partellus in CPM 8, CPM 13, CPM 15, CPM 18 and CML 345, thus could be used in insect resistance breeding program. These studies could also be useful for detailed understanding on metabolic pathways regulating biochemical defense and up- and down-regulation of associated genes in plant defense against biotic stresses.

Genome-Wide Association Analysis Identifies Resistance Loci for Bacterial Leaf Streak Resistance in Rice (Oryza sativa L.).

Bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) is one of the most devastating diseases in rice production areas, especially in humid tropical and subtropical zones throughout Asia and worldwide. A genome-wide association study (GWAS) analysis conducted on a collection of 236 diverse rice accessions, mainly indica varieties, identified 12 quantitative trait loci (QTLs) on chromosomes 1, 2, 3, 4, 5, 8, 9 and 11, conferring resistance to five representative isolates of Thai Xoc. Of these, five QTLs conferred resistance to more than one Xoc isolates. Two QTLs, qBLS5.1 and qBLS2.3, were considered promising QTLs for broad-spectrum resistance to BLS. The xa5 gene was proposed as a potential candidate gene for qBLS5.1 and three genes, encoding pectinesterase inhibitor (OsPEI), eukaryotic zinc-binding protein (OsRAR1), and NDP epimerase function, were proposed as candidate genes for qBLS2.3. Results from this study provide an insight into the potential QTLs and candidate genes for BLS resistance in rice. The recessive xa5 gene is suggested as a potential candidate for strong influence on broad-spectrum resistance and as a focal target in rice breeding programs for BLS resistance.

Gene Pyramiding for Achieving Enhanced Resistance to Bacterial Blight, Blast, and Sheath Blight Diseases in Rice.

Bacterial blight, blast, and sheath blight are the commonest diseases causing substantial yield loss in rice around the world. Stacking of broad-spectrum resistance genes/QTLs into popular cultivars is becoming a major objective of any disease resistance breeding program. The varieties ASD 16 and ADT 43 are the two popular, high yielding, and widely grown rice cultivars of South India, which are susceptible to bacterial blight (BB), blast, and sheath blight diseases. The present study was carried out to improve the cultivars (ASD 16 and ADT 43) through introgression of bacterial blight (xa5, xa13, and Xa21), blast (Pi54), and sheath blight (qSBR7-1, qSBR11-1, and qSBR11-2) resistance genes/QTLs by MABB (marker-assisted backcross breeding). IRBB60 (xa5, xa13, and Xa21) and Tetep (Pi54; qSBR7-1, qSBR11-1, and qSBR11-2) were used as donors to introgress BB, blast, and sheath blight resistance into the recurrent parents (ASD 16 and ADT 43). Homozygous (BC3F3 generation), three-gene bacterial blight pyramided (xa5 + xa13 + Xa21) lines were developed, and these lines were crossed with Tetep to combine blast (Pi54) and sheath blight (qSBR7-1, qSBR11-1, and qSBR11-2) resistance. In BC3F3 generation, the improved pyramided lines carrying a total of seven genes/QTLs (xa5 + xa13 + Xa21 + Pi54 + qSBR7-1 + qSBR11-1 + qSBR11-2) were selected through molecular and phenotypic assay, and these were evaluated for resistance against bacterial blight, blast, and sheath blight pathogens under greenhouse conditions. We have selected nine lines in ASD 16 background and 15 lines in ADT 43 background, exhibiting a high degree of resistance to BB, blast, and sheath blight diseases and also possessing phenotypes of recurrent parents. The improved pyramided lines are expected to be used as improved varieties or used as a potential donor in breeding programs. The present study successfully introgressed Pi54, and qSBR QTLs (qSBR7-1, qSBR11-1, and qSBR11-2) from Tetep and major effective BB-resistant genes (xa5, xa13, and Xa21) from IRBB60 into the commercial varieties for durable resistance to multiple diseases.

Screening of sweetpotato germplasm collections for sweetpotato weevil (Cylas spp.) resistance in Tanzania

Weevil damage caused by sweetpotato weevil (Cylas spp.) is a major constraint to sweetpotato production in Tanzania due to a lack of improved varieties with durable resistance. The objective of this study was to screen sweetpotato germplasm collections for weevil resistance and to select the best parents to be used in resistance breeding. Field studies involving 96 sweetpotato genotypes were conducted at two weevil hotspot sites in Western Tanzania using a 12 x 8 lattice design with three replications at each site. Data collected included yield and yield related traits, weevil reaction and weevil damage score. The tested genotypes differed significantly (P &lt; 0.01) for sweetpotato storage root number, root weight, root infestation and root damage score. Weevil infestation on storage roots significantly (P ≤0.05) correlated with total root number (r = 0.38) and weevil damage score (r = 0.79). Marketable root weight and total root weight were significantly correlated with infested root weight each with r = 0.45. The study identified nine sweetpotato genotypes expressing resistance and 10 genotypes with moderate resistance to weevil. Five genotypes including Magunhwa, Chuchu ya Nesi, Rugomoka, Tumauma and New Kawogo were selected with weevil resistance and desirable yield and yield-related traits. These genotypes can be used in future weevil resistance breeding programs of sweetpotato in Western Tanzania or related agro-ecologies.

Resistance assessment and biochemical responses of maize genotypes against Rhizoctonia solani f. sp. sasakii Exner causing Banded leaf and sheath blight disease

Maize (Zea mays L.) is a staple food in many parts of the world. In addition to being used as grain, animal feed, production of corn ethanol, starch, syrup etc., it has been widely consumed as a vegetable in the form of baby corn and sweet corn. Banded leaf and sheath blight (BLSB) is one of the major diseases affecting maize and is caused by Rhizoctonia solani f. sp. sasakii Exner. In the experiment forty six maize inbreds were screened for their reaction against the BLSB pathogen following artificial inoculation. Two inbred lines namely, EV1417 and CML-323 produced resistant and moderately resistant disease reaction respectively. Biochemical studies indicated the presence of a high level of pre-infectional barriers in the resistant line. Further, higher level of defense related enzymatic activities of peroxidase and poly phenol oxidase were detected in the resistant inbred line. After 48 h of inoculation, in comparison to highly susceptible EV1428, electrolyte leakage was found to be stabilized in EV1417 and CML-323. This study clearly establishes the presence of effective pre-infection barriers and induced biochemical defence mechanisms operating in the resistant inbred line. The identified resistant line EV1417 is further being used in BLSB disease resistance breeding programmes.

Whole genome analysis of the koa wilt pathogen (Fusarium oxysporum f. sp. koae) and the development of molecular tools for early detection and monitoring

BackgroundDevelopment and application of DNA-based methods to distinguish highly virulent isolates of Fusarium oxysporum f. sp. koae [Fo koae; cause of koa wilt disease on Acacia koa (koa)] will help disease management through early detection, enhanced monitoring, and improved disease resistance-breeding programs.ResultsThis study presents whole genome analyses of one highly virulent Fo koae isolate and one non-pathogenic F. oxysporum (Fo) isolate. These analyses allowed for the identification of putative lineage-specific DNA and predicted genes necessary for disease development on koa. Using putative chromosomes and predicted gene comparisons, Fo koae-exclusive, virulence genes were identified. The putative lineage-specific DNA included identified genes encoding products secreted in xylem (e. g., SIX1 and SIX6) that may be necessary for disease development on koa. Unique genes from Fo koae were used to develop pathogen-specific PCR primers. These diagnostic primers allowed target amplification in the characterized highly virulent Fo koae isolates but did not allow product amplification in low-virulence or non-pathogenic isolates of Fo. Thus, primers developed in this study will be useful for early detection and monitoring of highly virulent strains of Fo koae. Isolate verification is also important for disease resistance-breeding programs that require a diverse set of highly virulent Fo koae isolates for their disease-screening assays to develop disease-resistant koa.ConclusionsThese results provide the framework for understanding the pathogen genes necessary for koa wilt disease and the genetic variation of Fo koae populations across the Hawaiian Islands.

Pyrenophora tritici-repentis population structure in the Republic of Kazakhstan and identification of wheat germplasm resistant to tan spot.

Pyrenophora tritici-repentis is a causative agent of tan spot in wheat. In recent years, there has been an increasing spread and harmfulness of wheat tan spot. The aim of the research was to study the racial composition of the P. tritici-repentis population in the Republic of Kazakhstan. A collection of 30 common wheat accessions, including promising lines and cultivars from Kazakhstan and CIMMYT–ICARDA, was assessed for resistance to P. tritici- repentis in a greenhouse and characterized using the Xfcp623 molecular marker, diagnostic for the Tsn1 gene. Monosporic isolates of P. tritici-repentis isolated from the southeastern region were assigned to certain races based on the manifestation of symptoms of necrosis/chlorosis on standard differentials (Glenlea, 6B662, 6B365). Five races of P. tritici-repentis have been identified, including races 1, 2, 3, 7 and 8. It has been shown that races 1 and 8 of P. tritici-repentis are dominant. As a result of the analysis of the frequency of occurrence of the P. tritici-repentis races, it was found that race 1 (50 %) producing Ptr ToxA and Ptr ToxB and race 8 (35 %) producing Ptr ToxA, Ptr ToxB and Ptr ToxC turned out to be dominant. From a practical point of view, of greatest interest are 16 wheat samples, which demonstrated resistance to race 1 and confirmed insensitivity to Ptr ToxA in a molecular screening. These include eight Kazakhstani (4_PSI, 10204_2_KSI, 10204_3_KSI, 10205_2_KSI, 10205_3_KSI, 605_SP2, 632_SP2, Dana) and seven foreign lines (KR11-20, KR11-03, KR11-9014, 11KR-13, KR11-9025, KR12-07, GN-68/2003). The results of this study are of interest in wheat breeding programs for tan spot resistance.

Potato dry rot disease: current status, pathogenomics and management.

Potato dry rot disease caused by Fusarium species is a major threat to global potato production. The soil and seed-borne diseases influence the crop stand by inhibiting the development of potato sprouts and cause severe rots in seed tubers, table and processing purpose potatoes in cold stores. The symptoms of the dry rot include sunken and wrinkled brown to black tissue patches on tubers having less dry matter and shriveled flesh. Fungal infection accompanied by toxin development in the rotten tubers raises more concern for consumer health. The widespread dry rot causing fungal species (Fusarium graminearum) is reported to have a hemibiotrophic lifestyle. A cascade of enzymes, toxins and small secreted proteins are involved in the pathogenesis of these hemibiotrophs. With the availability of the genome sequence of the most devastating species Fusarium sambucinum, it is important to identify the potential pathogenicity factors and small secreted proteins that will help in designing management strategies. Limited resistant cultivars and the emergence of fungicide-resistant strains have made it more threatening for potato cultivation and trade. Several novel fungicide molecules (Azoxystrobin, chlorothalonil and fludioxonil), are found very effective as tuber treatment chemicals. Besides, many beneficial bioagents and safer chemicals have shown antibiosis and mycoparasitism against this pathogen. Germplasm screening for dry rot resistance is important to assist the resistance breeding program for the development of resistant cultivars. This review aims to draw attention to the symptomatology, infection process, pathogenomics, the role of toxins and management approaches for potato dry rot disease, which is very much critical in designing better management strategies.

Antixenosis, tolerance and genetic analysis of some rice landraces for resistance to Nilaparvata lugens (Stål.)

• Six rice landraces of West Bengal exhibited a high level of resistance to BPH. • Phenotypic reactions of the resistant landraces were equivalent to Ptb33. • Genetic diversity was observed within the landraces with similar phenotypic expression. • Resistant landraces can be used in resistance breeding programme to develop BPH resistant varieties. Twenty-six rice landraces from West Bengal, India were evaluated for antixenosis and tolerance against brown planthopper (BPH) biotype 4 at the Bidhan Chandra Krishi Viswavidyalaya (BCKV), West Bengal. High levels of resistance were observed in six landraces, namely Badshabhog, Gamra, Haldichuri, Janglijata, Kalabhat and Khara. These phenotypically resistant rice landraces including Ptb33 exhibited lowest feeding rate, fecundity, nymphal and adult preference, survival, plant dry weight loss per mg of BPH dry weight produced (PDWL), and higher functional plant loss index (FPLI), more days to wilt and unhatched eggs compared with the susceptible check Swarna. All the landraces were classified into four major clusters at 10 unit distance by the scale of similarity during genetic diversity analysis through 21 gene-linked SSR markers of BPH resistance. Some phenotypically resistant landraces were gathered under the major cluster I indicating their analogous genetic history, while some were grouped with susceptible landraces exhibiting their genetic variation. The resistant landraces can be used as potential donors in the breeding programme for the development of rice varieties with resistance to BPH.

Reactions of selected bean cultivars and accessions to Iranian populations of Meloidogyne javanica and race 2 of M. incognita

Breeding programs for nematode resistance in common bean require the identification and characterization of resistance sources among genotypes against local nematode populations. The reactions of 24 genotypes of dry and snap beans from Iran and CIAT (International Center for Tropical Agriculture, Colombia) were investigated against the Iranian population of Meloidogyne javanica and M. incognita race 2 under greenhouse conditions. To this objective, two independent experiments for each nematode species (inoculum = 5000 Juvenile 2 and eggs/plant) were carried out. Individual plants were harvested to determine the two most reliable values of nematode resistance indices viz. resistance index (RI) that was calculated using combined values of galling and egg mass production indices, and the percent reduction of reproduction index that was generated using nematode reproduction factor. Among the genotypes, Alabama # 1 showed resistance to both nematode species with RI = 14.5 and 11.5 for M. javanica and M. incognita race 2, respectively. In contrast, all the other 23 genotypes were susceptible and/or highly susceptible to M. javanica (RI = 132.75–162) and M. incognita race 2 (RI = 113–162) in two experiments, respectively. Several genotypes including Carioca, Enxofre, Mulatinho Comun, and Rio Doce, previously reported as resistant or moderately resistant to different M. incognita populations, resulted highly susceptible to both nematode populations from Iran. This study showed different responses of bean genotypes to distinct geographical populations/strains of root-knot nematodes.

QTL-seq analysis of powdery mildew resistance in a Korean cucumber inbred line.

QTL mapping and RT-PCR analyses identified the CsGy5G015660 as a strong powdery mildew resistance candidate gene and natural variation of CsGy5G015660 allele was observed using 115 core germplasm. Powdery mildew (PM) is among the most serious fungal diseases encountered in the cultivation of cucurbits. The development of PM-resistant inbred lines is thus of considerable significance for cucumber breeding programs. In this study, we applied bulked segregant analysis combined with QTL-seq to identify PM resistance loci using F2 population derived from a cross between two Korean cucumber inbred lines, PM-R (resistant) and PM-S (susceptible). Genome-wide SNP profiling using bulks of the two extreme phenotypes identified two QTLs on chromosomes 5 and 6, designated pm5.2 and pm6.1, respectively. The two PM resistance loci were validated using molecular marker-based classical QTL analysis: pm5.2 (30% R2 at LOD 11) and pm6.1 (11% R2 at LOD 3.2). Furthermore, reverse transcriptase-PCR analyses, using genes found to be polymorphic between PM-R and PM-S, were conducted to identify the candidate gene(s) responsible for PM resistance. We found that transcripts of the gene CsGy5G015660, encoding a putative leucine-rich repeat receptor-like serine/threonine-protein kinase (RPK2), showed specific accumulation in PM-R prior to the appearance of disease symptoms, and was accordingly considered a strong candidate gene for PM resistance. In addition, cleaved amplified polymorphic sequence markers from CsGy5G015660 were developed and used to screen 35 inbred lines. Natural variation in the CsGy5G015660 allele was also observed based on analysis of a core collection of 115 cucumber accessions. Our results provide new genetic insights for gaining a better understanding of the genetic basis of PM resistance in cucumber, and pave the way for further utilization in cucumber PM resistance breeding programs.

Field response of wheat genotypes to spot blotch under different sowing dates at Rampur, Chitwan, Nepal

Wheat spot blotch, caused by Bipolaris sorokiniana (Sacc.) Shoemaker has emerged as an important fungal disease for its economic losses in Nepalese wheat production system due state of poor resistance to spot blotch exacerbated by terminal heat stress in popular released wheat varieties. Thus it has engendered a dire need for identification of new robust and improved varieties with spot blotch resistance, suited to different sowing conditions. A field experiment was conducted at premises of Agriculture and Forestry University, Rampur to elucidate the field response of twenty wheat genotypes under different sowing conditions (early- 25th November, normal- 10th December, and late- 25th December) to spot blotch by using Split plot design, each treatment with three replicates, during 2017-2018. The analysis of variance revealed highly significant interaction (p&lt;0.01) between the sowing dates and genotypes for the disease progress. A higher yield penalty due to significantly higher disease severity under late-sown wheat cropping was observed due to warmer conditions later in the season. Genotypes viz., NL 1207 (168.5 and 416.77) and BL 4341 (185.97 and 428.8) outrivaled other test genotypes with substantially lower mean area under disease progress curve (AUDPC) values based on flag leaf and penultimate leaf infection, and higher yield (3.23 and 3.02 t/ha), respectively, and thus could be effectively utilized as robust progenitor in spot blotch resistance breeding programs. Our findings revealed that the simultaneous adoption of early sowing and resistant wheat genotypes could be a promising and economic avenue to reduce the disease pressure leading reduced yield penalties.

Selection for bean fly (Ophiomyia spp) resistance and agronomic performance in selected common bean (Phaseolus vulgaris L.) accessions

The bean fly (Ophiomyia spp) is one of several yield limiting insect pests of common bean (Phaseolus vulgaris L.) in eastern and southern Africa. High performing common bean cultivars with the bean fly resistance, good agronomic traits and market-preferred attributes are yet to be developed in the region. The objective of this study was to evaluate the bean fly resistance and agronomic performance of common bean accessions adapted to the eastern and southern African regions and to select parental lines for breeding. Ninety-nine common bean accessions were evaluated in bean fly hotspot areas in two locations in Malawi during the 2018 and 2019 growing seasons. Damage severity (BDS), plant mortality rate (PMR) and pupa count (PC) were measured to evaluate resistance to the bean fly. The following agro-morphological traits were assessed: the length between first internode and fifth internode at first flowering (FIL), number of nodes at the first flower (NFF), stem diameter (SD) at 50% flowering stage, days to 50% flowering (DTF), days to 90% physiological maturity (DTM), number of pods per plant (NPP), number of seed per pod (NSP) and grain yield in kg ha−1 (GYD). The analysis of variance revealed significant genotypic variation (p < 0.05) for both bean fly resistance and agro-morphological traits for common bean improvement. About 67.13% variation was explained by the first three principal components associated with BDS, PMR, DTF, SD, NPP, NSP and GYD. Phenotypic correlations between bean-fly resistance traits and grain yield were significant (p < 0.05) and negative, implying that direct selection for bean fly resistant genotypes could improve GYD. Twelve genotypes, namely, A55, A222, A429, Sinoni, ALB 196, MW3954, SIN526, CZ114-50, SCR63, MW3917, ALB133 and A344 showed high grain yield and exhibited resistance to the bean fly. These genotypes will be useful as parental lines for resistance breeding programs in the region.

Validation of marker-assisted selection in soybean breeding program for pod shattering resistance

Significant yield losses are caused by pod shattering during the harvest of domesticated crop plants. The phenotype evaluation of pod shattering requires fully grown plants, and it is a labor-intensive and time-consuming procedure. The purpose of this study was to test the applicability of previously identified KSS-SNP5 SNP marker on chromosome 16 in the marker assisted selection (MAS) system for pod shattering in soybean breeding programs. For this research, TaqMan SNP assay was successfully developed to detect the A/G allele of the KSS-SNP5 marker in the breeding materials, including two breeding stages, F2:3 populations, and yield trial stage breeding lines. The MAS prediction accuracy was calculated by comparing the genotyping data from the TaqMan assay with the phenotype data from the dry-oven method. The total MAS prediction accuracy was 92.5% and 96.2% in two F2:3 populations and breeding lines, respectively and 85% and 96% accuracy were shown in severe conditions. In this study, we confirmed that the KSS-SNP5 TaqMan probe tightly linked to pod shattering is effective to select a resistant line. Based on these results, we propose that the marker tightly linked to pod shattering can be of valuable use in soybean breeding program for the development of pod shattering-resistant cultivars.

Disease incidence and severity in cowpea lines evaluated for resistance to single and multiple infections of endemic viruses in Nigeria

ABSTRACT Cowpea (Vigna unguiculata (L.) Walp) is susceptible to several viruses in West Africa. Cowpea viral diseases are mainly controlled through the use of resistant cultivars. Co-infection with more than one virus is frequent in the fields and the resultant synergistic effect often compromises host resistance identified by screening against individual viruses under field or controlled conditions. In this study, eight improved cowpea breeding lines, identified as resistant to single infections and a susceptible cultivar (Ife Brown), were evaluated for their reactions to single and multiple infections of three viruses endemic in West Africa; viz., bean common mosaic virus-blackeye cowpea mosaic strain (BCMV-BlCM), southern bean mosaic virus (SBMV), and cucumber mosaic virus (CMV). Cowpea seedlings were inoculated with these viruses singly or in combination. Disease incidence and severity were recorded at weekly intervals for eight weeks. Virus infection was confirmed by enzyme-linked immunosorbent assay or reverse transcription-polymerase chain reaction. Systemic mosaic, vein-banding, and stunting were observed on inoculated plants. Mixed infection increased symptom severity and the highest severity was found in plants co-infected with CMV. Phenotyping against mixed-infections was more promising for estimating host resistance response in cowpea than single infections. Based on virus incidence and severity, lines IT97K-1069-6 and IT04K-405-5 were found to be resistant to SBMV, whereas IT99K-1060 and IT98K-503-1 were susceptible to the three viruses. IT-98 K-1092-1 was found to be resistant to BCMV and SBMV and tolerant to CMV under mixed inoculation scenario. Cowpea line IT-98 K-1092-1 is, thus, the best resistance source for use in virus resistance-breeding programs.

A multilocational evaluation of blast resistance in a diverse panel of finger millet in India

Blast of finger millet, Pyricularia grisea, is an economically important disease causing significant loss of production worldwide. Use of resistant cultivar is the most economical way for management of the disease. Identification of stable sources of resistance is of utmost importance to develop varieties against the highly variable pathogen. In this study one hundred-fifteen finger millet genotypes including 108 germplasm of African and Asian origin and a few improved cultivars were evaluated for finger and neck blast resistance across three locations representing major finger millet areas in India during 2016, 2017 and 2018. Evaluation was conducted under natural field conditions, supplemented with artificial inoculation of earhead with blast pathogen at pre-anthesis stage. Disease severity was assessed using a 1–9 disease rating scale. Twenty-nine of the 115 genotypes showed resistance either for finger or neck blast, while six showed combined resistance to both. Stability analysis of those 29 genotypes revealed that five (IE Nos., 2883, 2871, 6240, 2710 and GE3767) were stable for both finger and neck blast resistance. They also possess desirable agronomic characters like medium plant height (100–110 cm), medium maturity (106–115 days) and semi-compact (top of finger incurved) earhead shape. This paper reports stable sources of finger and neck blast resistance in finger millet, which will serve as important donor in a finger millet resistance breeding programme.