Identification of Drought Tolerant Rice (Oryza Sativa L.) Genotypes with Asian and African Backgrounds.

Drought is among the major abiotic stresses on rice production that can cause yield losses of up to 100% under severe drought conditions. Neither of the rice varieties currently grown in Burundi can withstand very low and irregular precipitation. This study identified genotypes that have putative quantitative trait loci (QTLs) associated with drought tolerance and determined their performance in the field. Two hundred and fifteen genotypes were grown in the field under both drought and irrigated conditions. Genomic deoxyribonucleic acid (DNA) was extracted from rice leaves for further genotypic screening. The results revealed the presence of the QTLs qDTY12.1, qDTY3.1, qDTY2-2_1, and qDTY1.1 in 90%, 85%, 53%, and 22% of the evaluated genotypes, respectively. The results of the phenotypic evaluation showed a significant yield reduction due to drought stress. Yield components and other agronomic traits were also negatively affected by drought. Genotypes having high yield best linear unbiased predictions (BLUPs) with two or more major QTLs for drought tolerance, including IR 108044-B-B-B-3-B-B, IR 92522-45-3-1-4, and BRRI DHAN 55 are of great interest for breeding programs to improve the drought tolerance of lines or varieties with other preferred traits.

Heat Stress Tolerance in Rice (Oryza sativa L.): Identification of Quantitative Trait Loci and Candidate Genes for Seedling Growth Under Heat Stress.

Productivity of rice, world's most important cereal is threatened by high temperature stress, intensified by climate change. Development of heat stress-tolerant varieties is one of the best strategies to maintain its productivity. However, heat stress tolerance is a multigenic trait and the candidate genes are poorly known. Therefore, we aimed to identify quantitative trait loci (QTL) for vegetative stage tolerance to heat stress in rice and the corresponding candidate genes. We used genotyping-by-sequencing to generate single nucleotide polymorphic (SNP) markers and genotype 150 F8 recombinant inbred lines (RILs) obtained by crossing heat tolerant "N22" and heat susceptible "IR64" varieties. A linkage map was constructed using 4,074 high quality SNP markers that corresponded to 1,638 recombinationally unique events in this mapping population. Six QTL for root length and two for shoot length under control conditions with 2.1-12% effect were identified. One QTL rlht5.1 was identified for "root length under heat stress," with 20.4% effect. Four QTL were identified for "root length under heat stress as percent of control" that explained the total phenotypic variation from 5.2 to 8.6%. Three QTL with 5.3-10.2% effect were identified for "shoot length under heat stress," and seven QTL with 6.6-19% effect were identified for "shoot length under heat stress expressed as percentage of control." Among the QTL identified six were overlapping between those identified using shoot traits and root traits: two were overlapping between QTL identified for "shoot length under heat stress" and "root length expressed as percentage of control" and two QTL for "shoot length as percentage of control" were overlapping a QTL each for "root length as percentage of control" and "shoot length under heat stress." Genes coding 1,037 potential transcripts were identified based on their location in 10 QTL regions for vegetative stage heat stress tolerance. Among these, 213 transcript annotations were reported to be connected to stress tolerance in previous research in the literature. These putative candidate genes included transcription factors, chaperone proteins (e.g., alpha-crystallin family heat shock protein 20 and DNAJ homolog heat shock protein), proteases, protein kinases, phospholipases, and proteins related to disease resistance and defense and several novel proteins currently annotated as expressed and hypothetical proteins.

Nor-hopanes from Zanha africana root bark with toxicity to bruchid beetles.

Zanha africana (Radlk.) Exell (Sapindaceae) root bark is used by farmers throughout sub-Saharan Africa to protect stored grain from bruchid beetles, such as Callosobruchus maculatus. Chloroform, methanol and water extracts of Z. africana root bark inhibited oviposition and caused significantly higher mortality of C. maculatus at a rate of application equivalent to that applied by farmers compared to control insects. The chloroform extract contained nor-hopanes rarely found in plants of which seven were isolated, one of which was previously known. Two of the most abundant nor-hopanes 3ß,6ß-dihydroxy-7ß-[(4-hydroxybenzoyl)oxy]-21αH-24-norhopa-4(23),22(29)-diene and 3ß,6ß-dihydroxy-7ß-[(4-hydroxybenzoyl)oxy]-24-norhopa-4(23),17(21)-diene were toxic to and reduced oviposition of C. maculatus in a dose dependent manner. Z. africana root bark is rich in insecticidal compounds that account for its effective use by smallholder farmers as an alternative to conventional insecticides.