Disna Ratnasekera

Seed-Mediated Gene Flow Promotes Genetic Diversity of Weedy Rice within Populations: Implications for Weed Management

Increased infestation of weedy rice—a noxious agricultural pest has caused significant reduction of grain yield of cultivated rice (Oryza sativa) worldwide. Knowledge on genetic diversity and structure of weedy rice populations will facilitate the design of effective methods to control this weed by tracing its origins and dispersal patterns in a given region. To generate such knowledge, we studied genetic diversity and structure of 21 weedy rice populations from Sri Lanka based on 23 selected microsatellite (SSR) loci. Results indicated an exceptionally high level of within-population genetic diversity (He = 0.62) and limited among-population differentiation (Fst = 0.17) for this predominantly self-pollinating weed. UPGMA analysis showed a loose genetic affinity of the weedy rice populations in relation to their geographical locations, and no obvious genetic structure among populations across the country. This phenomenon was associated with the considerable amount of gene flow between populations. Limited admixture from STRUCTURE analyses suggested a very low level of hybridization (pollen-mediated gene flow) between populations. The abundant within-population genetic diversity coupled with limited population genetic structure and differentiation is likely caused by the considerable seed-mediated gene flow of weedy rice along with the long-distance exchange of farmer-saved rice seeds between weedy-rice contaminated regions in Sri Lanka. In addition to other effective weed management strategies, promoting the application of certified rice seeds with no weedy rice contamination should be the immediate action to significantly reduce the proliferation and infestation of this weed in rice ecosystems in countries with similar rice farming styles as in Sri Lanka.

Dietary species richness as a measure of food biodiversity and nutritional quality of diets

Significance Current research linking biodiversity and human diets has used metrics without justification from a nutritional point of view. Diet species richness, or a count of the number of different species consumed per day, assesses both nutritional adequacy and food biodiversity of diets for women and children in rural areas. The positive association of food species richness with dietary quality was observed in both the wet and the dry season. Food biodiversity contributes to diet quality in vulnerable populations in areas with high biodiversity. Reporting the number of species consumed during dietary assessment provides a unique opportunity to cut across two critical dimensions of sustainable development—human and environmental health—and complements existing indicators for healthy and sustainable diets. Biodiversity is key for human and environmental health. Available dietary and ecological indicators are not designed to assess the intricate relationship between food biodiversity and diet quality. We applied biodiversity indicators to dietary intake data from and assessed associations with diet quality of women and young children. Data from 24-hour diet recalls (55% in the wet season) of n = 6,226 participants (34% women) in rural areas from seven low- and middle-income countries were analyzed. Mean adequacies of vitamin A, vitamin C, folate, calcium, iron, and zinc and diet diversity score (DDS) were used to assess diet quality. Associations of biodiversity indicators with nutrient adequacy were quantified using multilevel models, receiver operating characteristic curves, and test sensitivity and specificity. A total of 234 different species were consumed, of which <30% were consumed in more than one country. Nine species were consumed in all countries and provided, on average, 61% of total energy intake and a significant contribution of micronutrients in the wet season. Compared with Simpson’s index of diversity and functional diversity, species richness (SR) showed stronger associations and better diagnostic properties with micronutrient adequacy. For every additional species consumed, dietary nutrient adequacy increased by 0.03 (P < 0.001). Diets with higher nutrient adequacy were mostly obtained when both SR and DDS were maximal. Adding SR to the minimum cutoff for minimum diet diversity improved the ability to detect diets with higher micronutrient adequacy in women but not in children. Dietary SR is recommended as the most appropriate measure of food biodiversity in diets.

SUSTAINABLE MAIZE (Zea mays L.) PRODUCTION UNDER DROUGHT STRESS BY UNDERSTANDING ITS ADVERSE EFFECT, SURVIVAL MECHANISM AND DROUGHT TOLERANCE INDICES

Maize is an essential dietary component in human food and in animal feed formulation. With the rising trend of global climate change, grain yield and quality losses of maize are expected to increase, because of various biotic and abiotic stress in all over the world. Among these, drought is most considerable one; it remarkably influences growth and yield traits of maize. Hence, the improvement of drought tolerant maize genotypes has potential to stabilize and even though increases the grain yield of maize. Therefore, developing cultivars tolerant to drought stress is a challenge for breeders. There are two ways to mitigate drought stress in maize production, either by developing and practicing improved drought * Corresponding author KEYWORDS

Biopesticides Research: Current Status and Future Trends in Sri Lanka

Sri Lanka is a tropical country equally having rich diversity of arthropods including natural enemies, economic pests, and indigenous plants majority with unique chemical properties. Because of the substantial losses due to pests and diseases, plant protection remains an essential issue in agriculture production in the country. There is increasing concern over synthetic pesticide usage due to their adverse long-term effects on human health, environment, and natural pest management systems. As an eco-friendly alternate, the importance of biopesticides in raising agricultural productivity is well recognized in Sri Lanka. Biopesticides are quiet popular among farming community due to their unique features, viz., safety, limited host range or target specificity, the absence of toxic residues, eco-friendly nature, and ease of application. Biopesticides have diverse modes of action and hence resistance development in pests is slower/negligible. Currently, plant powders, nonvolatile and volatile oils, and plant crude extracts are commercially available for management of insect pests and nematodes. Further, several bacterial and fungal biopesticides have shown promising results for the efficient management of plant pathogens in Sri Lanka.

A calcium dependent protein kinase involves H2O2 mediated guard cell signaling in Arabidopsis.

Drought is a major threat for plant growth and productivity. Plants lose over 90% of water by transpiration through stomatal pores. The cytosolic free Ca2+ elevated in guard cells in response to stress stimuli triggers stomatal closure. The plant-specific calcium-dependent protein kinases (CDPKs) play important roles in regulating downstream components of calcium signaling. In this study the biological function of Arabidopsis calcium dependent protein kinase, CPK8, in response to ABA signaling in guard cells was characterized. The plants of TDNA insertion mutant of cpk8 were more sensitive to drought stress than wild-type plants. The GUS staining studies confirmed that CPK8 expressed in leaves, specifically in guard cells. RT-PCR analysis showed that CPK8 expression was induced in response to drought stress. Further, pre-opened cpk8 stomata failed to close in response to H2O2 and Ca2+, which is consistent with the inability of cpk8 plants to reduce water loss upon drought. The drought susceptibility and stomatal impairment in response to H2O2 and Ca2+ of the cpk8 implicated that CPK8 plays a role in cellular environment in the control of H2O2 homeostasis and also as a compulsory molecule in the transduction of H2O2 signal in guard cells in response to drought stress. Tropical Agricultural Research and Extension 16(1): 2013: page 7-14