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Twenty-eight hybrids produced from diallel crossing excluding reciprocals among eight parents were studied along with the parents for combining ability for yield and 12 yield components. The study revealed the importance of both additive and non-additive gene effects in governing yield and most of the yield components with preponderance of non-additive gene action for most of the yield components. The analysis of variance for combining ability indicated that mean square due to general combining ability (GCA) was significant for all the characters except for number of tillers/m2, panicle length (cm), number of spikelets /panicle, number of fertile spikelets / panicle, 1000 – grain weight(g) and grain yield(tha-1) which was non significant. Mean square due to specific combining ability (SCA) were significant for all the characters except for spikelets/panicle, fertile spikelets/panicle, 1000-grain weight(g) and grain yield(tha-1) which were non significant. This suggests the importance of both additive and non-additive gene effects in the materials under study. The parent WAB 450-I-B-163-41 was found to be a good general combiner. The hybrids WAB 56-144-FX x WAB 56-100, WAB 450-1-B-163-41 x IRAT 317,WAB 450 -1-B163-41 x IR 47-701-6-3-1, WAB 450-1-B-163-41 x IRAT 239,WAB 35-1-FX x WAB 56 -100, WAB 35 -1-FX x WAB 56-100, IRAT 239 x WAB 56 -100 and IRAT 317 x IRAT 239 have shown significant favorable (SCA) effect for yield and different yield components. Since non- additive/dominance components were higher than the additive components for all the characters in both F1 and F2 generations, bi parental mating and/or reciprocal recurrent selection could be used for genetic improvement of these characters. Keywords: Diallel analysis, combining ability, additive and non additive gene effects, GCA effect, SCA effect.

The storage rot of yam ( Dioscorea spp ) starts from the field to the storage barn. Fungi pathogens affecting yam tubers are controlled by either synthetic pesticides or plant extracts.The following plant extracts, Vernonia amygdalina (bittter leaf), Azadirachta indica (neem), Ocimum gratissimum (nchuanwu), Pergularia spp . (utazi), Citrus aurantifolia (lime), Allium sativum (gallic), and Capsicum annum (red pepper) were used to control the rot of yam (caused by Aspergillus niger). The ethanol extracts of the test plants were observed to have higher fungitoxic ability than the water extracts on A. niger , which was isolated from the rotten yam tubers. Ethanol extracts of A. indica and O. gratissimum were observed to have the highest percentage fungi growth inhibition, having 68.8% and 65.2% respectively, while A. sativum, and C. annum had the lowest with 36.3% and 40.6% respectively. A. indica was also observed to have the highest severity and A. sativum had the lowest. However, yam tubers which were treated 2 days before inoculation were observed to have more inhibitory effect on the fungi pathogen than those treated 2 days after inoculation. Keywords : storage-rot, yam-tubers, plant-extracts, fungal-pathogens, severity International Journal of Agriculture and Rural Development Vol. 6 2005: 74-80