Performance of testers with contrasting provitamin A content to evaluate provitamin A maize for resistance to Aspergillus flavus infection and aflatoxin production

Open Access JournalIn sub-Saharan Africa (SSA), millions of people depend on maize as a primary staple. However, maize consumers in SSA may be exposed to malnutrition due to vitamin A deficiency (VAD) and unsafe aflatoxin levels, which can lead to serious economic and public health problems. Provitamin A (PVA) biofortified maize has been developed to alleviate VAD and may have additional benefits such as reduced aflatoxin contamination. In this study, maize inbred testers with contrasting PVA content in grain were used to identify inbred lines with desirable combining ability for breeding to enhance their level of resistance to aflatoxin. Kernels of 120 PVA hybrids generated by crossing 60 PVA inbreds with varying levels of PVA (5.4 to 51.7 µg/g) and two testers (low and high PVA, 14.4 and 25.0 µg/g, respectively) were inoculated with a highly toxigenic strain of Aspergillus flavus. Aflatoxin had a negative genetic correlation with β-carotene (r = −0.29, p 0.5). Eight inbreds had combined significant negative GCA effects for aflatoxin accumulation and spore count with significant positive GCA effects for PVA. Five testcrosses had combined significant negative SCA effects for aflatoxin with significant positive SCA effects for PVA. The high PVA tester had significant negative GCA effects for aflatoxin, lutein, β-carotene, and PVA. The study identified lines that can be used as parents to develop superior hybrids with high PVA and reduced aflatoxin accumulation. Overall, the results point out the importance of testers in maize breeding programs to develop materials that can contribute to controlling aflatoxin contamination and reducing VAD

Reaction of Dioscorea alata (water yam) to anthracnose disease in Nigeria

Anthracnose disease, caused by the pathogen Collectotrichum gloeosporioides Penz., is a serious challenge to the cultivation of Dioscorea alata, a major source of food and income for millions of farm households in the tropics. Five breeder’s lines and eighteen landraces of D. alata from IITA’s germplasm collection were screened in the field in three agroecological zones (southern guinea savanna, derived savannah and the humid forest) of Nigeria for two years. The objective was to study their reactions to anthracnose disease and investigate the influences of environment (E) and genotype x environment (G x E) interactions on these using the Additive Main Effects and Multiplicative Interaction (AMMI) model. Environments (E), obtained as location x year combination, genotypes (G) and G x E interactions were highly significant (P<0.01) for severity of anthracnose disease and accounted for 48, 26.2 and 25.8% of the treatment (G x E combination) sum of squares, respectively. Incidence and severity of foliar symptoms were assessed on three occasions during each growing season. The disease was most severe at Umudike in the humid forest, followed by Ibadan (derived savannah) and Mokwa (southern guinea savannah). The severity was also higher in 1999 across all locations than in 2000. TDa 289 and TDa 294 were identified as the most resistant genotypes. TDa 297, TDa 9500328, TDa 9500197 and TDa 9500010 were stable in their reactions to anthracnose disease across the environments. These lines could be useful in breeding for increased and more stable resistance to anthracnose disease in yam breeding programmes

Genetic diversity of Colletotrichum gloeosporioides in Nigeria using amplified fragment length polymorphismA (AFLP) markers

Colletotrichum gloeosporioides is the causal agent of yam anthracnose disease in Nigeria. Differential cultivars and amplified fragment length polymorphic DNA markers were used to assess the extent of genetic diversity among 39 isolates of the pathogen. Fourteen (14) pathotypes of the pathogen were identified based on inoculation of a differential set of Dioscorea alata genotypes of which pathotype P11 was the most virulent attacking all differential D. alata host genotypes, while pathotype P8 was the least virulent. 52% of the isolates were avirulent, 23% were slightly virulent and 25% were virulent. Amplified fragment length polymorphism (AFLP) analysis confirmed genetic variation among the C. gloeosporioides isolates and was effective in establishing genetic relationships between them. However, the grouping of the isolates based on AFLP analysis was not directly related to virulence groups or geographical origin of the isolates. The genetic variation in C. gloeosporioides is important in choosing strategies to develop durable resistanc