Effect of ambient levels of ozone on photosynthetic components and radical scavenging system in leaves of African cowpea varieties

Tropospheric ozone (O3), a main component of photochemical oxidants, adversely affects not only human health but also vegetation. To clarify the long-term effects of ambient levels of tropospheric ozone (O3) on photosynthetic components and radical scavenging system in the leaves of cowpea ( Vigna unguiculata L.), two African varieties, Blackeye and Asontem, were grown in open-top chambers and exposed to filtered air (FA), non-filtered air (NF) or non-filtered air with additional O3 of approximately 50 nl l-1. Ambient levels of O3 significantly reduced chlorophyll concentration, quantum yield and activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), thus contributing to the reduction in net photosynthetic rate at the reproductive growth stage of both varieties; with no significant variety difference in the sensitivity to O3. The O3-induced significant reduction in catalase activity was observed in Blackeye at vegetative and reproductive growth stages; and in Asontem at reproductive growth stage. On the other hand, exposure to O3 significantly increased ascorbate peroxidase activity in Blackeye at reproductive stage and did not significantly affect that in Blackeye at vegetative growth stage and that in Asontem at both growth stages. At reproductive growth stage, activities of monodehydroascorbate reductase and glutathione reductase were significantly increased by the exposure to O3 in both varieties. The results obtained in this study suggest that, although ascorbate peroxidase, monodehydroascorbate reductase and glutathione reductase played important roles in scavenging O3-induced reactive oxygen species in the leaves, radical scavenging ability of these enzymes is not sufficient to avoid detrimental effects of ambient levels of O3 on photosynthesis in both African cowpea varieties.

ADAPTATION OF INTRODUCED MUNGBEAN GENOTYPES IN UGANDA

Mungbean ( Vigna radiata (L.) Wilczek) is an important source of nutrients and income for smallholder farmers in East Africa. Mungbean production in countries like Uganda largely depends on landraces, in the absence of improved varieties. In order to enhance productivity, efforts have been underway to develop and evaluate mungbean varieties that meet farmers’ needs in various parts of the country. This study was conducted at six locations in Uganda, to determine the adaptability of introduced mungbean genotypes, and identify mungbean production mega-environments in Uganda. Eleven genotypes (Filsan, Sunshine, Blackgram, Mauritius1, VC6148 (50-12), VC6173 (B-10),Yellowmungo, KPS1, VC6137(B-14),VC6372(45-60),VC6153(B-20P) and one local check were evaluated in six locations during 2013 and 2014. The locations were; National Semi Arid Resources Research Institute (NaSARRI), Abi Zonal Agricultural Research and Development Institute (AbiZARDI),Kaberamaido variety trial center, Kumi variety trial center, Nabuin Zonal Agricultural Research and Development Institute (NabuinZARDI), and Ngetta Zonal Agricultural Research and Development Institute (NgettaZARDI). G × E interactions were significant for grain yield. Through GGEBiplot analysis, three introduced genotypes (Filsan, Blackgram and Sunshine) were found to be stable and high yielding, and therefore, were recommended for release. The six test multi-locations were grouped into two candidate mega-environments for mungbean production (one comprising of AbiZARDI and Kaberamaido and the other comprising of NaSARRI, NabuinZARDI, Kumi, and NgettaZARDI). National Semi Arid Resources Research Institute (NaSARRI) was the most suitable environment in terms of both discriminative ability and representativeness and therefore can be used for selection of widely adaptable genotypes.