Pectobacterium atrosepticum (Pa), P. carotovorum subsp. brasiliensis (Pcb) and Dickeya spp. cause soft rot of potato worldwide. Plants respond to bacterial invasion by activating defense responses associated with accumulation of several enzymes and inhibitors, which prevent pathogen infection. This study focused on the role of polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), chlorogenic acid and total soluble phenols in imparting resistance to soft rot pathogens.Seven and eleven varieties grown by farmers in South Africa and Zimbabwe, respectively, were used in the study. The results showed significantly higher (P < 0.001) enzyme activity of PPO and PAL as well as higher concentrations of chlorogenic acid and total soluble phenols in Vanderplank, Pentland Dell, M69/11, Romano, M59/20 and Ngadze, E. Plant Disease 2 Mondial Zw . PAL activity increased significantly with time in all varieties and the highest activity was recorded 8 h after cutting. The resistance of the varieties was correlated w i t h h i g h P P O a n d P A L e n z y m e a c t i v i t y a s w e l l a s i n c r e a s e d c o n c e n t r a t i o n s o f chlorogenic acid and total soluble phenols. PPO, POD and PAL activities increased significantly in wounded and inoculated tubers. These findings show that PAL, PPO, POD, chlorogenic acid and total soluble phenols play a role in imparting resistance to potato soft rot infection.

Nutrients such as boron, nitrogen and calcium stimulate the production of phenols.This research focuses on the role of calcium in increasing phenol metabolism in potato peels and the ensuing tuber resistance to soft rot pathogens was investigated.Two field experiments were conducted at the University of Zimbabwe campus plots

Grain‐filling rate (GFR), effective grain‐filling duration (EGFD), and total grain‐filling duration (TGFD) are important physiological traits of maize (Zea mays L.) grain yield (GY) formation. To devise effective breeding strategies, the genetic nature of these traits is a prerequisite for improvement in early maturing maize. A study was conducted at CIMMYT‐Zimbabwe using an α‐lattice design with two replications in two environments to investigate the genetic variability of grain‐filling traits in 18 early maturing tropical maize inbred lines derived from CIMMYT germplasm. Highly significant differences were observed for GY, thousand‐grain weight (TGW), GFR, EGFD, TGFD, kernels per row (KR), and rows per cob (RC). The broad‐sense coefficient of genetic determination (the fixed parent equivalent of broad‐sense heritability) was above 70% for all of the traits. The highest GY was obtained from the inbred line T032‐30 (79.2 g plant–1) and the lowest from inbred line CML506 (37.6 g plant–1), respectively. Therefore, selecting for higher GFR and longer TGFD, especially the EGFD, can increase GY of early maize without extending days to physiological maturity (DPM).

Early planting of bambara groundnuts (Vigna subterranea L. Verdc) in the southern Africa enables farmers to fetch premium prices before the markets are flooded with produce from the main summer growing period. However, adaptation of the crop outside the main growing season has not been studied in Zimbabwe. Therefore, this study evaluated 20 varieties at four planting dates covering contrasting temperatures and daylength, at Harare Research Station, during 2000/2001. Planting date was the main plot factor replicated three times and cultivar the subplot. Standard agronomic practices were followed and adequate moisture supplied through supplementary irrigation. Both the planting dates and variety main effects were significant (P<0.05) for yield and most of the secondary traits. Planting date x genotype interaction (G x E) effects were not significant (P<0.05) for yield, suggesting that cultivars were relatively yield stable. However, G x E effects were significant (P<0.05) for days to 50% emergence and pod count plant -1 . Differences among varieties were attributable to genotypic effects and different photothermal conditions. August and September planting dates resulted in high dry pod yield. Varieties BS599, BS537, V2-17, BS520, and Variety-10, had high relative yield, and were the most promising for off-season planting.Key Words: Genotype x environment, planting date, Vigna subterranea RÉSUMÉ La sémis précoce des arachides bambara (Vigna subterranea l. Verdc) permet aux agriculteurs de se procurer de bénéfices importants avant que les marchés ne soient inondés par la production réalisée en période de croissance normale. Toutefois, l'adaptation de la culture en dehors de la saison de croissance principale n'avaiit pas été étudiée au Zimbabwe. Par conséquent, une étude avait été menée afin d'évaluer 20 variétés à quatre différentes dates de sémis couvrant des températures variées et la longueur de la journée, à la station de recherche de Harare, au cours de 2000/2001. La date de plantation avait été le facteur principal répliquées trois fois et le cultivar le facteur subordonné. Les pratiques agronomiques standard avaient été observées et une humidité adéquate fournie par le biais d'une irrigation supplémentaire. Les dates de plantation aussi bien que et les variétes comme effets principaux avaient été significatives (P<0.05) pour le rendement et la plupart des traits secondaires. Les effets de la date de sémis x interaction génotypique (G x E) n'étaient pas significatifs (P<0,05) pour le rendement, ce qui donne à penser que les cultivars étaient de rendement relativement stable. Toutefois, les effets G x E étaient significatifs (P<0,05) pour les jours à 50 % d'émergence et le comptage de gousse par plante. Les différences entre les variétés étaient attribuables aux effets génotypiques et aux différentes conditions photothermales. Les dates de plantation d'Août et Septembre, ont entraîné un rendement élevé en gousse sec. Les variétés BS599, BS537, V2-17, BS520, et variety-10, avaient un rendement relativem...

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