Heat stress is one of the production constraints for tomato (Solanum lycopersicum L.) due to unfavorable, above optimum temperatures. This research was undertaken to evaluate growth and fruit yield of tomato genotypes under three contrasting growing conditions (i.e., optimal temperature in field-, high temperature in field- and high temperature in greenhouse conditions) to determine their relative heat tolerance. Eleven tomato genotypes, including two local check varieties, were evaluated, and data on growth and yield were measured and analyzed. The interactions between the genotypes and growing conditions for all yield traits were significant. In general, the performance of tomato under optimal temperature field conditions was better than under high temperature field- and greenhouse conditions. Genotypes CLN1621L, CLN2026D, CLN3212C, and KK1 had consistently greater fruit yield per plant in all growing conditions. Although the local genotype, Neang Tamm, had lower yield under optimal conditions, it performed moderately well under high temperature field- and high temperature greenhouse conditions, and yield decrease under high temperature condition was minimal. Genotype CLN1621L had stable fruit setting compared to other genotypes under high temperature conditions. Since fruit setting and yield are important traits for heat tolerance, genotypes CLN1621L and Neang Tamm are potential candidates for breeding programs focused on improved yield and heat stress tolerance.

Key message A candidate gene responsible for higher grain zinc accumulation in rice was identified, which was probably associated with a partial defect in anther dehiscence. Abstract Zinc (Zn) is an essential mineral element in many organisms. Zn deficiency in humans causes various health problems; therefore, an adequate dietary Zn intake is required daily. Rice, Oryza sativa , is one of the main crops cultivated in Asian countries, and one of the breeding scopes of rice is to increase the grain Zn levels. Previously, we found that an Australian wild rice strain, O. meridionalis W1627, exhibits higher grain Zn levels than cultivated rice, O. sativa Nipponbare, and identified responsible genomic loci. An increase in grain Zn levels caused by one of the loci, qGZn9a , is associated with fertility reduction, but how this negative effect on grain productivity is regulated remains unknown. In this study, we artificially trimmed spikelets on the flowering day and found that a reduction in number of seeds was associated with an increase in the grain Zn levels. We also found that a partial defect in anther dehiscence correlated with the increase in grain Zn levels in plants carrying the W1627 chromosomal segment at qGZn9a in a Nipponbare genetic background. Among eight candidate genes in the qGZn9a region, three were absent from the corresponding region of W1627; one of these, Os09g0384900 , encoding a DUF295 protein with an unknown function, was found to be specifically expressed in the developing anther, thereby suggesting that the gene may be involved in the regulation of anther dehiscence. As fertility and grain Zn levels are essential agronomic traits in rice, our results highlight the importance of balancing these two traits. Supplementary Information The online version contains supplementary material available at 10.1007/s00122-021-03873-4.

Cultivated rice (Oryza sativa L.) was domesticated from the Asian wild species O. rufipogon. Compared with cultivated rice, wild rice has spikelets/seeds with long barbed awns. In order to evaluate the role of awns in wild rice, four seed groups with different awn lengths (full, half, quarter and no awns) were prepared, and the following seed dispersal movements were investigated under simulated natural conditions as observed in the tropical Asian habitat: (1) seed detachment from the parent plant; (2) falling angle of mature seed; (3) ability to slip into small spaces; (4) horizontal movement on the ground and (5) horizontal movement in water. As a result, awns were found to enhance the detachment of matured seeds from the panicles in the initial seed dispersal step. They regulated vertical orientation in the air, and the vertical form may enable seeds to squeeze to the ground. The awned seeds also showed advantages in horizontal movements on the ground and in the water. In most of the experiments, seeds with full awns showed the best performance for seed dispersal, suggesting that wild rice keeps long awns to survive under natural conditions. Since seed awning is dominantly controlled by wild functional alleles at several loci, wild rice may be able to prevent a drastic reduction of awn length.

More than half-century ago, local rice varieties were collected from Indochinese countries (Cambodia, Thailand, Laos, and Vietnam). Of these, 162 local varieties were examined for 7 grain-size traits: seed length/width/thickness, brown rice length/width/thickness, and 100-seed weight. Since these traits varied considerably, a survey of functional mutations was performed in the genes related to these traits. In total, 19 markers (12 InDel and 7 dCAPS markers) were used to investigate the mutations at 14 grain-size loci of GW2, GS2, qLGY3, GS3, GL3.1, TGW3, GS5, GW5, GS6, TGW6, GW6a, GLW7, GL7, and GW8. Significant allele effects were observed with six markers detecting base substitution mutations at GW2 and GS3 and insertion/deletion mutations at GS5, GW5, and GW6a, suggesting that these mutations might have affected the grain trait and caused variation among local varieties in the Indochinese countries. In addition to grain size, the hull color, grain color, and glutinosity were also examined using a survey of loss-of-function mutations at major responsible loci. Most phenotypes were reflected based on functional mutations at these loci. Since the local varieties have wide genetic variation, they are important genetic resources for future rice breeding.