Veronica N.E. Uzokwe

Novel loci for field resistance to black-streaked dwarf and stripe viruses identified in a set of reciprocal introgression lines of rice (Oryza sativa L.)

Rice black-streaked dwarf virus (RBSDV) and stripe virus (RSV) are the two chronic viral diseases causing great damage to rice (Oryza sativa L.) production in China, and both are transmitted by the small brown planthopper (SBPH, Laodelphaxstriatellus Fallén). Quantitative trait loci (QTL) affecting field resistance to these two viral diseases were identified using QTL mapping software in a set of reciprocal introgression lines derived from the cross between Lemont and Teqing. A panel of 119 landraces was used for marker confirmation and allele mining. A total of 17 quantitative resistance loci (QRL) for the infection incidences of RBSDV and RSV were discovered and belong to 16 regions on all chromosomes except chromosome 12. Among them, 12 QRL were confirmed by association mapping, and many novel alleles at these loci were mined from the set of landraces. Only one region was found to be responsible for the genetic overlap between the field resistance against RBSDV and RSV, which was reported to be associated with SBPH resistance. The favorable alleles at the above novel and/or overlapping loci should be effective for marker-assisted selection breeding for resistance against the two diseases and the insect. Different strategies of varietal development and effective deployment against the two viral diseases are also discussed.

Optimization Modeling for Conjunctive Use Planning of Surface Water and Groundwater for Irrigation

AbstractThe continuous increase in global population and simultaneous decrease in good-quality water resources emphasize the need of conjunctive use of groundwater and surface-water resources for irrigation. The optimal allocation of water resources can be achieved by employing an appropriate optimization technique. This paper presents an overview of the different programming techniques used for the conjunctive use planning and management of irrigated agriculture. Past papers on the applications of different programming techniques for the conjunctive use of different water sources are grouped into four categories: linear programming, nonlinear programming, dynamic programming, and genetic algorithms. Conclusions are provided based on this review, which could be useful for all stakeholders.

Genetic Analysis of Cold Tolerance at Seedling Stage and Heat Tolerance at Anthesis in Rice (Oryza sativa L.)

A set of 240 introgression lines derived from the advanced backcross population of a cross between a japonica cultivar, Xiushui 09, and an indica breeding line, IR2061, was developed to dissect QTLs affecting cold tolerance (CT) at seedling stage and heat tolerance (HT) at anthesis. Survival rate of seedlings (SRS) and spikelet fertility (SF), the index traits of CT and HT, showed significant differences between the two parents under stresses. A total of four QTLs (qSRS1, qSRS7, qSRS11a and qSRS11b) for CT were identified on chromosomes 1, 7, 11, and the Xiushui 09 alleles increased SRS at all loci except qSRS7. Four QTLs for SF were identified on chromosomes 4, 5, 6, and 11. These QTLs could be classified into two major types based on their behaviors under normal and stress conditions. The first was QTL expressed only under normal condition; and the second QTL was apparently stress induced and only expressed under stress. Among them, two QTLs (qSF4 and qSF6) which reduced the trait difference between heat stress and normal conditions must have contributed to HT because of their obvious contribution to trait stability, and the IR2061 allele at the qSF6 and the Xiushui 09 allele at the qSF4 improved HT, respectively. No similar QTL was found between CT at seedling stage and HT at anthesis. Therefore, it is possible to breed a new variety with CT and HT by pyramiding the favorable CT- and HT-improved alleles at above loci from Xiushui 09 and IR2061, respectively, through marker-assisted selection (MAS).

Women's empowerment in traditional food value chains at the micro-level: evidence from cassava smallholder farming in Tanzania

ABSTRACT Empowering women improves household food productivity and security. We examined women’s empowerment within the cassava value chain according to the five domains of empowerment of the Women’s Empowerment in Agriculture Index, using data from 228 respondents in Tanzania. Disempowerment indices for women and men were 0.95 and 0.14, respectively. Women were disempowered in the production, leadership, and time domains. Women were empowered in the resources domain, which entailed joint ownership and decision making. Marital status and educational levels were significantly associated with women’s empowerment. Policies to improve women’s empowerment should focus on securing ownership of resources and access to credit.

Performance of cassava brown streak disease-tolerant varieties in Zanzibar, Tanzania

Cassava is an important staple food in subtropical regions; however, its production is adversely affectedby cassava brown streak disease and poor soil fertility. Five improved and two local cassava varieties wereevaluated for three seasons across two sites in Kizimbani, Zanzibar. Highly significant differences were detectedamong varieties, sites and years for fresh shoot yield, and fresh root yield. For cassava brown streak diseaseassociated root necrosis, highly significant differences were detected only between varieties but not sites oryears. On average, the site that had a slightly higher soil nitrogen level recorded ∼126% higher fresh root yield. Two improved varieties, ‘Kizimbani’ and ‘Machui’, produced significantly higher fresh root yields than the bestlocal variety, ‘Mwari’. However, the local variety ‘Boma’ is preferred by farmers in Zanzibar because it has betterfresh consumption qualities than ‘Mwari’. ‘Boma’ is highly susceptible to cassava brown streak disease andproduces a poor yield. The four released varieties, ‘Kama’, ‘Kizimbani’, ‘Mahonda’ and ‘Machui’ were superior to‘Boma’ in cassava brown streak disease resistance and yield. Further, soil fertility improvement and productionsystem intensification are needed to enhance productivity.