A survey of sorghum downy mildew in sorghum in the Sudano-Sahelian Savanna zones of Nigeria

An extensive survey was conducted across the 13 states constituting the Sudan and Sahel savanna agro-ecological zones of Nigeria to determine the occurrence and distribution of sorghum downy mildew in sorghum during the 2008 growing season. The survey was conducted at two different stages of the crop development; seedling and dough stage. The first survey was in early July while the second was carried out in late September. Three farmers’ fields were critically investigated at every stop on a road system. During the first survey, a total of 97 farmers’ fields in 36 locations were investigated while 110 sorghum fields in 37 locations were visited in the second survey. Average incidence (%) of the disease was obtained from a sample of 100 plants selected using simple random sampling technique from each of the three farms visited per stop. Results of the survey (16.20 and 9.64% and 3.28 and 1.16% during the first and second visits in the Sudan and Sahel savanna AEZs respectively) indicated that the disease was present only at the seedling stage and virtually absent at flowering stage .In the areas where it was noticed at the juvenile stage the incidence was more prevalent in the Sudan than in the sahel savanna regions. The results also revealed that there was a relationship between soil type (which was mostly sandy loam) and disease incidence. Disease incidence was relatively higher on sandy loam soil than other soil types. The prevalence was generally low, but efforts should be made towards controlling the spread of the disease further. Farmers should be advised to use improved cultural practices like early sowing, seed dressing with the sole aim of reducing the disease. Keywords: sorghum downy mildew, incidence, distribution, Sudan and Sahel savanna agroecological zone

Screening of Sorghum Genotypes fFor Resistance to Loose Smut in Nigeri

One hundred and four sorghum genotypes were screened under field conditions for loose smut disease using the hypodermic stem injection artificial inoculation technique. The experiment was laid out on a randomized complete block design (RCBD) with two replications. The results of the trial indicated that only twenty nine genotypes (27.9 %) showed loose smut symptom at varying degrees of incidence and with varying severity. Both disease incidence and severity were significantly different (P<0.01) among sorghum genotypes. More than 70 % (73 genotypes) were found to be immune (I) and 5.76 % (six) genotypes were highly resistant (HR) which included, SSV2008030, SSV2008031, SSV2008034, SSV2008066, SSV20080075, and SSV2008088 and nineteen (18.27%) were very susceptible (VS) genotypes. There was no moderately susceptible genotype obtained from the experiment. The results have shown that there are some promising sorghum genotypes that are resistant to the disease and could therefore be introduced to farmers and sorghum breeders for further breeding as well as multi-locational trials.Keywords; field screening, hypodermic injection, loose smut, sorghum varieties, Sudan savann

Genic SNP markers and legume synteny reveal candidate genes underlying QTL for Macrophomina phaseolina resistance and maturity in cowpea [Vigna unguiculata (L) Walp.]

<p>Abstract</p> <p>Background</p> <p><it>Macrophomina phaseolina </it>is an emerging and devastating fungal pathogen that causes significant losses in crop production under high temperatures and drought stress. An increasing number of disease incidence reports highlight the wide prevalence of the pathogen around the world and its contribution toward crop yield suppression. In cowpea [<it>Vigna unguiculata </it>(L) Walp.], limited sources of low-level host resistance have been identified, the genetic basis of which is unknown. In this study we report on the identification of strong sources of host resistance to <it>M. phaseolina </it>and the genetic mapping of putative resistance loci on a cowpea genetic map comprised of gene-derived single nucleotide polymorphisms (SNPs) and amplified fragment length polymorphisms (AFLPs).</p> <p>Results</p> <p>Nine quantitative trait loci (QTLs), accounting for between 6.1 and 40.0% of the phenotypic variance (R²), were identified using plant mortality data taken over three years in field experiments and disease severity scores taken from two greenhouse experiments. Based on annotated genic SNPs as well as synteny with soybean (<it>Glycine max</it>) and <it>Medicago truncatula</it>, candidate resistance genes were found within mapped QTL intervals. QTL <it>Mac-2 </it>explained the largest percent R²and was identified in three field and one greenhouse experiments where the QTL peak co-located with a SNP marker derived from a pectin esterase inhibitor encoding gene. Maturity effects on the expression of resistance were indicated by the co-location of <it>Mac-6 </it>and <it>Mac-7 </it>QTLs with maturity-related senescence QTLs <it>Mat-2 </it>and <it>Mat-1</it>, respectively. Homologs of the <it>ELF4 </it>and <it>FLK </it>flowering genes were found in corresponding syntenic soybean regions. Only three <it>Macrophomina </it>resistance QTLs co-located with delayed drought-induced premature senescence QTLs previously mapped in the same population, suggesting that largely different genetic mechanisms mediate cowpea response to drought stress and <it>Macrophomina </it>infection.</p> <p>Conclusion</p> <p>Effective sources of host resistance were identified in this study. QTL mapping and synteny analysis identified genomic loci harboring resistance factors and revealed candidate genes with potential for further functional genomics analysis.</p

The Effects Of Leaf Spot Diseases And Staking On Yield And Yield Attributes Of Winded Bean Psophocarpus Tetragonolobus (L.Dc.)

Leaf spot was identified as the major disease of winged bean (Psophocarpus tetragonolobus) in the Zaria area of Northern Nigeria. The disease was induced by (Cercospora psophocarpicola, Macrophomina phaseolina, Septosphaeria prolata, Phomopsis sp., Phoma sp., Curvularia ovoidea, Alteraria longissima and Lasiodiplodia theobromae. The severity of the leaf spot disease caused significant reduction in fresh pod length, dry pod yield and grain yield, but did not affect the number of pods produced per plant. Staked plants performed better than unstaked plants in terms of number of pods per plant, length of dry and fresh pods, dry pod and grain yield. Staking however, did not have any effect on the severity of leaf spot disease complex of the winged bean. It is therefore, advised that winged bean plants be staked for a better performance.Journal of Applied Chemistry and Agricultural Research Vol. 7 2000-2001: pp. 42-4

Field evaluation of improved cowpea lines for resistance to bacterial blight, virus and striga under natural infestation in the West African Savannas

The average productivity of cowpea in the existing traditional systems is low due to a complex of biotic and abiotic stresses. The biotic factors include insect pests, parasitic plants, and viral, fungal andbacterial diseases. Concerted efforts are being made to develop improved cowpea varieties with combined resistance to these constraints. Twenty five cowpea lines including two local land-races were grown at three locations in the first year (2002) and at six locations in the second year (2003) in Nigeria and Niger for field screening for resistance to Bacterial blight. Many of the improved varieties had significantly higher grain and fodder yields than the local checks. There was genotype x environment interactions for grain and fodder yields. About 44% of the varieties tested were resistant to bacterial blight while 20% showed moderate resistance and others were susceptible. Bacterial blight was more important in the Sahel, and several improved cowpea breeding lines, IT98K-506-1, IT97K-1113-7, IT97K- 1069-6, IT97K-1092-2, IT97K-1069-5, IT98K-131-2 and IT97K-568-18 produced higher grain and fodderyields than the other varieties and showed combined resistance to the disease. These varieties should therefore be evaluated on-farm for onward release to farmers where there seed types meet the farmerspreferred seed type other wise they can be used as parent lines as source of important genes for resistant to the diseases and high grain and fodder yields