Studies of the genetics of inheritance of stem rust resistance in bread wheat

Pgt race TTKSK (Ug99) has a wide virulence range with respect to currently grown wheat cultivars worldwide. Aspects of migration, mutation, recombination and selection in the pathogen have led to previously deployed stem rust resistance genes being ineffective. Race TTKSK has further evolved to acquire virulence for resistance genes such as Sr24 (race Ug99 + Sr24) and Sr36 (Ug99 + Sr36). Five resistant wheat lines (KSL-2, KSL-3, KSL-5, KSL-12 and KSL-19) which were resistant in tests during 2008, 2009 and 2010 were used as parents in crosses with stem rust susceptible line CACUKE to develop genetic populations for determining the inheritance of resistance to stem rust. F3 populations were evaluated at KARI Njoro in the 2012 off season and 2012 to 2013 main season. The adult plant stem rust responses were scored using the modified Cobb’s scale. The F2:3 lines of population(s) exhibiting qualitative variation were grouped as homozygous resistant (HR), segregating (Seg) and homozygous susceptible (HS). Heavy disease pressure was present during the cropping seasons with the check CACUKE displaying 90% susceptibility. Chi square analysis revealed that the segregation data in the parent KSL-2 did not deviate significantly from the single gene model (1:2:1) suggesting that the resistance to stem rust is conditioned by a single dominant gene. The Chi square test also revealed that the stem rust resistance in the parents KSL-3, KSL-5, KSL-12 and KSL-19 was conditioned by two genes. The families from the KSL-2 and KSL-3 crosses also segregated for the presence of the pseudo black chaff implying that the Sr2 gene could be present in the background of these wheat parents. The superior transgressive segregants identified in these crosses will be used in breeding.Keywords: Genetic, wheat, gene, resistanceAfrican Journal of Biotechnology Vol. 12(21), pp. 3153-315

DEVELOPMENT OF WHEAT GERMPLASM FOR STEM RUST RESISTANCE IN EASTERN AFRICA

Wheat ( Triticum aestivum ) rust outbreak is the primary production constraint in Eastern Africa. Ethiopia, Kenya and Uganda are hot spots for the epidemic of rusts, due to higher rates of evolution of new pathogen races, especially of the virulent stem rust (Puccinia graminis) race, Ug99. The objective of this study was to identify sources of resistance to the major pathotypes of stem rust prevalent in some countries of Eastern Africa. Three hundred and six elite breeding lines, selected and advanced at the Wheat Regional Centre of Excellence (WRCoE) in Ethiopia, were planted in stem rust hot spot areas of the country (Arsi-Robe) and Kenya (Njoro) under natural infections. Stem rust scores of 18, 25.8 and 56.2% of lines at Arsi-Robe; and 35, 49 and 16.7% of lines at Njoro were resistant to moderately resistant, intermediate and moderately susceptible to susceptible category, respectively. Overall coefficient of infection (ACI) at Arsi-Robe (24) was greater than that of Njoro (13), indicating higher disease pressure in Ethiopia than Kenya. Among the lines, 67% at Njoro and 49% at Arsi Robe showed good levels of resistance, with a severity less than 20%. However, only 32% of the lines showed a good level of resistance (<20% severity) in both locations. These lines could have combined resistance to the multiple stem rust races prevailing at both locations. Generally, most of the lines, which showed better resistance at Njoro were susceptible at Arsi-Robe.La rouille de la tige chez le bl\ue9 ( Triticum aestivum ) est l\u2019un des plus importants probl\ue8mes rencontres dans la production du bl\ue9 en Afrique de l\u2019Est. L\u2019Ethiopie, le Kenya et l\u2019Ouganda sont des pays \ue0 fort taux d\u2019\ue9pid\ue9mie de rouille de la tige. Ceci \ue0 cause du taux \ue9lev\ue9 de d\u2019agents pathog\ue8nes, ainsi que l\u2019apparition de nouveaux pathog\ue8nes, dont le plus redoutable (Puccinia graminis) race Ug99. L\u2019objectif de cette \ue9tude \ue9tait d\u2019identifier des sources de r\ue9sistance aux pathotypes majeurs de la rouille de tige qui sevit dans certains pays de l\u2019Afrique de l\u2019Est. Trois cent six lign\ue9es \ue9lites, s\ue9lectionn\ue9es au centre r\ue9gionale d\u2019excellence du bl\ue9 (WRCoE) en Ethiopie, ont \ue9t\ue9 plant\ue9es dans des zones a fort taux de pr\ue9valence de la rouille de tige en Ethiopie (Arsi-Robe) au Kenya (Njoro). Respectivement, 18, 25.8 et 56.2% des lign\ue9es a Arsi-Robe; et 35, 49 et 16.7% des lign\ue9es a Njoro se sont r\ue9v\ue9l\ue9es r\ue9sistantes ou mod\ue9r\ue9ment r\ue9sistantes, interm\ue9diaires, mod\ue9r\ue9ment susceptibles a susceptibles. En somme, le coefficient d\u2019infection (ACI) \ue0 Arsi-Robe (24) \ue9tait plus \ue9lev\ue9 qu\u2019\ue0 Njoro (13), ceci indique que la pression de la rouille de tige est plus \ue9lev\ue9e en Ethiopie qu\u2019au Kenya. Parmi les lign\ue9es \ue9valu\ue9es, 67% \ue0 Njoro et 49% a Arsi Robe sont exhibe des bons niveaux de r\ue9sistance, avec 20% de s\ue9v\ue9rit\ue9. N\ue9anmoins, seul 32% des lign\ue9es ont exhibe une bonne r\ue9sistance (<20% s\ue9v\ue9rit\ue9) dans les deux localit\ue9s. Ces lign\ue9es porteraient surement des g\ue8nes de r\ue9sistance multiple contre les diff\ue9rentes races de champignon pr\ue9sents dans les deux localit\ue9s. G\ue9n\ue9ralement, la plupart des lign\ue9es ayant exhibe une bonne r\ue9sistance a Njoro \ue9taient susceptible a Arsi-Robe

Developing a Mini-Core Collection in Finger Millet Using Multilocation Data

Finger millet [Eleusine coracana (L.) Gaertn.], among small millets, is the most important food crop in some parts of Asia and Africa. The grains are a rich source of protein, fi ber, minerals, and vitamins. A core collection of 622 accessions was developed. The aim of this study was to develop a mini-core collection using multilocational evaluation data of the core collection. Six hundred and twenty-two accessions together with six controls (four common and two location-specifi c) were evaluated for 20 morphological descriptors at fi ve agroecologically diverse locations in India during the 2008 rainy season. The experiment was conducted in α design with two replications at Patancheru and in augmented design with one of the six controls repeated after every nine-test entry at other locations. The hierarchical cluster analysis of data using phenotypic distances resulted in 40 clusters. From each cluster, ~10% or a minimum of 1 accession was selected to form a mini-core, which was comprised of 80 accessions. The comparison of means, variances, frequency distribution, Shannon–Weaver diversity index (H`), and phenotypic correlations revealed that the mini-core captured the entire diversity of the core collection. This mini-core collection is an ideal pool of diverse germplasm for identifying new sources of variation and enhancing the genetic potential of fi nger millet

Discovery and characterization of two new stem rust resistance genes in Aegilops sharonensis

Stem rust is one of the most important diseases of wheat in the world. When single stem rust resistance (Sr) genes are deployed in wheat, they are often rapidly overcome by the pathogen. To this end, we initiated a search for novel sources of resistance in diverse wheat relatives and identified the wild goat grass species Aegilops sharonesis (Sharon goatgrass) as a substantial reservoir of resistance to wheat stem rust. The objectives of this study were to discover and map novel Sr genes in Ae. sharonensis and to explore the possibility of identifying new Sr genes by genome-wide association study (GWAS). We developed two biparental populations between resistant and susceptible accessions of Ae. sharonensis and performed QTL and linkage analysis. In an F6 recombinant inbred line and an F2 population, two genes were identified that mapped to the short arm of chromosome 1Ssh, designated as Sr-1644-1Sh, and the long arm of chromosome 5Ssh, designated as Sr-1644-5Sh. The gene Sr-1644-1Sh confers a high level of resistance to race TTKSK (one of the Ug99 lineage races), while the gene Sr-1644-5Sh conditions strong resistance to TRTTF, another widely virulent race found in Yemen. Additionally, GWAS was conducted on 125 diverse Ae. sharonensis accessions for stem rust resistance. The gene Sr-1644-1Sh was detected by GWAS, while Sr-1644-5Sh was not detected, indicating that the effectiveness of GWAS might be affected by marker density, population structure, low allele frequency and other factors

Evaluation of resistance of spring durum wheat germplasm from Russia and Kazakhstan to fungal foliar pathogens

Spring durum wheat (Triticum durum) is an important crop in Russia and Kazakhstan. There are substantial yield losses due to fungal diseases. The research focused on host plant resistance to fungal diseases, and identifcation of the sources of multiple resistance which can be deployed in durum wheat breeding programs. Extensive environmental varietal testing experiments at places with diverse meteorological factors allows the selection of valuable material. In 2017 and 2018, a collection of 21 spring durum wheat accessions from the Kazakhstan-Siberian Network for Wheat Improvement (KASIB) was studied under high disease pressure. The following diseases were evaluated in three regions of Russia (Omsk, Altai and Samara), in Southern Kazakhstan and in Kenya: leaf, stem and yellow rusts, powdery mildew, glume blotch, tan spot and spot blotch. As the result, three breeding lines with multiple disease resistance to three rust species, powdery mildew and leaf blotches were identifed: Hordeiforme 178-05-02, Hordeiforme 05-42-12 and Hordeiforme 1591-21. Furthermore, the accessions resistant to rusts or spots were also identifed. Phytopathological studies and molecular marker analysis showed absence of genes Lr1, Lr3, Lr9, Lr10, Lr19/Sr25, Lr20/Sr15, Lr24/Sr24, Lr26/Sr31/Yr9/Pm8, Lr34/Sr57/Yr18 and Lr37/ Sr38/Yr17. Clustering of durum wheat accessions based on similarity in resistance and susceptibility revealed three main groups; accessions susceptible to all three rusts, those with some resistance to one or two rusts, and those with seedling resistance to leaf rust only