No abstract

Direct seeding of rice often results in poor crop establishment due to unlevelled fields, unpredicted heavy rains after sowing, and weed and pest invasion. Thus, it is important to develop varieties able to tolerate flooding during germination, also known as anaerobic germination (AG), to address these constraints. A study was conducted to identify QTLs associated with AG tolerance from an IR64/Kharsu 80A F 2:3 mapping population using 190 lines phenotyped for seedling survival under the stress. Genotyping was performed using a genomewide 384-plex Indica/Indica SNP set. Four QTLs derived from Kharsu 80A providing increased tolerance to anaerobic germination were identified: three on chromosome 7 ( qAG7.1 , qAG7.2 and qAG7.3 ) and one on chromosome 3 ( qAG3 ), with LOD values ranging from 5.7 to 7.7, and phenotypic variance explained (R 2 ) from 8.1% to 12.6%. The QTLs identified in this study can be further investigated to better understand the genetic bases of AG tolerance in rice, and used for marker-assisted selection to develop more robust direct-seeded rice varieties.

Crops with resilience to multiple climatic stresses are essential for increased yield stability. Here, we evaluate the interaction between two loci associated with flooding survival in rice ( Oryza sativa L.). ANAEROBIC GERMINATION 1 ( AG1 ), encoding trehalose 6‐phosphate phosphatase 7 ( TPP7 ), promotes mobilization of endosperm reserves to enhance the elongation of a hollow coleoptile in seeds that are seeded directly into shallow paddies. SUBMERGENCE 1 ( SUB1 ), encoding the ethylene‐responsive transcription factor SUB1A‐1 , confers tolerance to complete submergence by dampening carbohydrate catabolism, to enhance recovery upon desubmergence. Interactions between AG1/TPP7 and SUB1/SUB1A‐1 were investigated under three flooding scenarios using four near‐isogenic lines by surveying growth and survival. Pyramiding of the two loci does not negatively affect anaerobic germination or vegetative‐stage submergence tolerance. However, the pyramided AG1 SUB1 genotype displays reduced survival when seeds are planted underwater and maintained under submergence for 16 d. To better understand the roles of TPP7 and SUB1A‐1 and their interaction, temporal changes in carbohydrates and shoot transcriptomes were monitored in the four genotypes varying at the two loci at four developmental timeponts, from day 2 after seeding through day 14 of complete submergence. TPP7 enhances early coleoptile elongation, whereas SUB1A‐1 promotes precocious photoautotrophy and then restricts underwater elongation. By contrast, pyramiding of the AG1 and SUB1 slows elongation growth, the transition to photoautotrophy, and survival. mRNA‐sequencing highlights time‐dependent and genotype‐specific regulation of mRNAs associated with DNA repair, cell cycle, chromatin modification, plastid biogenesis, carbohydrate catabolism and transport, elongation growth, and other processes. These results suggest that interactions between AG1/TPP7 and SUB1/SUB1A‐1 could impact seedling establishment if paddy depth is not effectively managed after direct seeding.

Abstract. Panaligan AC, Baltazar MD, Alejandro GJD. 2020. Short Communication: Genetic polymorphism of registered and popularly cultivated coffee (Coffea spp.) in the Philippines using inter-simple sequence repeats markers. Biodiversitas 21: 4228-4233. Three Coffea species, namely Coffea arabica, Coffea canephora and Coffea liberica have been commercially cultivated in the Philippines. Genetic variability analysis of these species is important for the conservation of genetic resources and breeding programs. Hence, this study was carried out to identify polymorphic inter-simple sequence repeats (ISSR) markers and determine the genetic variation of these three commercially cultivated coffee species. Twenty-nine DNA samples from young coffee leaves were extracted and PCR amplified. Of the 29 primers used, seven produced clear and reproducible bands. In the 54 bands produced, 51 were polymorphic. The number of bands amplified by each primer varied from 5 to 12 with an average of 7.71 bands. Polymorphism percentage ranged from 80 to 100. This is the first time that ISSR markers were used to determine the genetic variation of coffee in the Philippines. The study demonstrated the efficiency of ISSR markers to assess genetic variation in cultivated coffee species. The ISSR markers were able to differentiate the coffee germplasm at the interspecific and intraspecific levels. These results suggest the potential of ISSR markers for genetic diversity analysis of commercial coffee and varietal identification of elite varieties using DNA fingerprinting.