No abstract

Breeding maize hybrids for drought tolerance would significantly reduce yield loss due to drought in southern Africa. Mode of gene action controlling yield and secondary traits was investigated by mating 27 inbred lines, in sets according to a North Carolina design II scheme. The resultant 72 experimental and eight commercial hybrids were evaluated in 8 · 10 a-lattice design with two replications, in four drought and two non-drought environments. Under drought conditions, only general combining ability (GCA) variance was significant for yield, indicating predominance of additive effects. In non-drought environments, both GCA and specific combining ability variances were significant for yield, indicating importance of additive and non-additive effects, respectively. Contributions of male (GCA m ) and female GCA (GCA f ) effects to hybrids varied depending on the trait and conditions. Superior GCA f to GCA m effects for yield under drought conditions, and for ASI, prolificacy and ear aspect under both drought and non-drought conditions, suggested that maternal effects might have modified these traits. Larger GCA m than GCA f for ASI and silking dates under normal conditions indicated that paternal genotypes played a greater role in determining these traits. Similar GCA m and GCA f for yield under normal conditions, silking and anthesis dates under drought indicated that both parents made similar contribution to hybrids. Possibly, complications due to modification of traits by cytoplasmic effects and cross-over G · E for yield might partly explain why only a few drought tolerant hybrids have been developed. Practical implications of these findings in breeding drought tolerance in maize are discussed.

This study was done to identify pesticide-biodegrading microorganisms and to characterize degradation rates. Bacillus safensis strain FO-36b, Bacillus subtilis subsp. inaquosorum strain KCTC13429, and Bacillus cereus strain ATCC14579 were isolated from pesticide-polluted soil in Sudan, separately incubated with each pesticide with periodic samples drawn for GC and GC-MS. Pesticide biodegradation followed a biphasic model. α and β half-lives (days) of chlorpyrifos, malathion, and dimethoate in B. safensis culture were 2.13, 4.76; 2.59, 5.66; and 9.5, 11.0, respectively. Values in B. subtilis and B. cereus cultures were 4.09, 9.45 and 4.33, 9.99 for chlorpyrifos; 2.99, 5.36 and 2.43, 4.71 for malathion; and 9.53, 15.11 and 4.16, 9.27 for dimethoate. No metabolite was detected in B. subtilis cultures, whereas a few were detected from B. safensis and B. cereus cultures. Bacterial efficiency can be ordered as B. safensis > B. subtilis > B. cereus for chlorpyrifos and B. cereus > B. subtilis > B. safensis for malathion and dimethoate.

Cowpea [<italic>Vigna unguiculata</italic> (L.) Walp.] productivity is low in the subsistence farming systems due to biotic, abiotic and socio-economic constraints. The objective of this study was to assess farmers’- perceived production constraints, preferred traits and the farming system of cowpea, and its implication for breeding in northern Namibia. A participatory rural appraisal studies was conducted across four selected regions of northern Namibia including Kavango East, Kavango West, Oshikoto and Omusati where the crop is predominantly cultivated. Primary data was collected using structured interviews involving 171 households. Results showed that 70.2% farmers grow local unimproved cowpea varieties and 29.8% used improved varieties either singly or in combination of two or three. About 62.6% of interviewed farmers reported low yields of cowpea varying from 100-599 kg/ha, while 6% achieved good grain harvests of 1500-1999 kg/ha. Most farmers (59.1%) produced cowpea for home consumption, while 23.4% indicated its food and market value. Field pests such as aphids (77.8%), leaf beetles (53.2%) and pod borers (60%) and bruchids (100%) were the major constraints. <italic>Striga gesnerioides</italic> and <italic>Alectra Vogelii</italic> (Benth) were the principal parasitic weeds reported by 79.5% cowpea farmers. Soil fertility levels were reported to be very low across regions and all farmers did not apply any fertilizers on cowpea. Farmers-preferred traits of cowpea included a straight pod shape (61.4%), a long pod size, bearing at least 10 seeds (68.4%), white grain colour (22.2%) and above ground biomass (42.1%). Inter-cropping of cowpea with sorghum or pearl millet was the dominant cowpea farming system in northern Namibia. 68.4% of farmers used a relatively smaller proportion of their land (<1 ha) for cowpea production while only 9.9% allocate more than 5 ha. Breeding for high grain yield and farmers-preferred traits and availability of seed and production input are the most important strategies to increase cowpea production and productivity by subsistence farmers in the northern regions of Namibia.

Breeding new and high performing cultivars with market-preferred traits take more than 10 years in the absence of an integrated pre-breeding programme. During the early phases of breeding a significant amount of time, space and resources are invested in the selection and genetic advancement stages after initial crosses are performed with parental genotypes. Speed breeding has the potential to reduce the time required for cultivar development, release and commercialization. The objective of this review was to present the key opportunities and challenges of speed breeding to guide pre-breeding and breeding programmes. Key challenges of speed breeding include: (a) access to suitable facilities, (c) staff trained in the protocol, (b) adopting major changes to breeding programme design and operations, and (d) the need for long-term funding. The current review highlights the potential advantages of speed breeding for the successful development and release of pure line cultivars in selfpollinated crops in ~5 years versus 8 to 10 years when using traditional methods.