Inheritance and Allelic Relationships of Alectra vogelii Benth. Resistance Genes in Cowpea Genotypes B301 and KVx414-22-2

Alectra vogelii Benth. is the second most important parasitic weed in cowpea [Vigna unguiculata (L.) Walp.] production in Burkina Faso. Several resistant varieties to this weed have been identified in the country among which are B301 and KVx414-22-2. The inheritance and allelic relationships of the resistance genes in the two varieties have not been studied with A. vogelii strains in Burkina Faso. The objective of this study was to determine the inheritance and allelic relationship of the resistance genes in B301 and KVx414-22-2. To determine the inheritance of the genes for resistance, the resistant varieties (B301 and KVx414-22-2) were each crossed to a susceptible variety IT82D-849 to generate F1 and F2 populations. For the allelic relationship study the two resistant genotypes were crossed among themselves to generate F1 and F2 offspring. The parents and their F1 and F2 progenies were screened in artificially infested pots with Alectra seed in a screen house at Kamboinsé Research Station in Burkina Faso. Resistance/susceptibility of genotypes was assessed by recording the number of emerged Alectra shoots. The data were subjected to the Chi-Square goodness-of-fit test for one, two and three genes segregation ratios. The results revealed that two independent dominant genes confer resistance in the variety B301 and a single dominant gene confers resistance in variety KVx414-22-2. The single dominant gene in KVx414-22-2 is non-allelic to the two genes in B301. The two resistance genes in variety B301 have already been named Rav1 and Rav2 whilst Rav3 is the name of the resistance gene in variety IT81D-994. Therefore, we propose the symbol Rav4 as the name for the resistance gene in variety KVx414-22-2.

Inheritance and Allelic Relationship Among Downy Mildew Resistance Genes in Pearl Millet

Pearl millet downy mildew (DM), caused by Sclerospora graminicola, is of serious economic concern to pearl millet farmers in the major crop-growing areas of the world. To study the inheritance and allelic relationship among genes governing resistance to this disease, three DM-resistant pearl millet lines (834B, IP 18294-P1, and IP 18298-P1) and one susceptible line (81B) were selected on the basis of disease reaction under greenhouse conditions against two isolates of S. graminicola (Sg 526-1 and Sg 542-1). Three resistant parents were crossed with the susceptible parent to generate F1, F2, and backcross BC1P1 (susceptible parent × F1) and BC1P2 (resistant parent × F1) generations for inheritance study. To carry out a test for allelism, the three resistant parents were crossed with each other to generate F1 and F2 generations. The different generations of these crosses were screened for disease reaction against two isolates (Sg 526-1 and Sg 542-1) by artificial inoculation under greenhouse conditions. The segregation pattern of resistance in the F2 and corresponding backcross generations revealed that resistance to DM is controlled by a single dominant gene in 834B and IP 18294-P1 and by two dominant genes in IP 18298-P1. A test for allelism inferred that a single dominant gene for resistance in 834B is nonallelic to that which governs resistance in IP 18294-1, whereas one of the two dominant genes for DM resistance in IP 18298-P1 against the test isolates is allelic to the gene for DM resistance in 834B and a second gene is allelic to the resistance gene present in IP 18294-P1.