Occurrence of chalkiness in rice is attributed to genetic and environmental factors, especially high temperature (HT). The HT induces heat stress, which in turn compromises many grain qualities, especially transparency. Chalkiness in rice is commonly studied together with other quality traits such as amylose content, gel consistency, and protein storage. In addition to the fundamental QTLs, some other QTLs have been identified which accelerate chalkiness occurrence under HT condition. In this review, some of the relatively stable chalkiness, amylose content, and gel consistency related QTLs have been presented well. Genetically, HT effect on chalkiness is explained by the location of certain chalkiness gene in the vicinity of high-temperature-responsive genes. With regard to stable QTL distribution and availability of potential material resources, there is still feasibility to find out novel stable QTLs related to chalkiness under HT condition. A better understanding of those achievements is essential to develop new rice varieties with a reduced chalky grain percentage. Therefore, we propose the pyramiding of relatively stable and nonallelic QTLs controlling low chalkiness endosperm into adaptable rice varieties as pragmatic approach to mitigate HT effect.
Tomato yellow leaf curl virus (TYLCV) responsible for tomato yellow leaf curl disease (TYLCD) causes a substantial decrease in tomato (Solanum lycopersicum L.) yield worldwide. The use of resistant variety as a sustainable management strategy has been advocated. Tremendous progress has been made in genetically characterizing the resistance genes (R gene) in tomato. Breeding tomato for TYLCV resistance has been based mostly on Ty-3 as a race-specific resistance gene by introgression originating from wild tomato species relatives. Improvement or development of a cultivar is achievable through the use of marker-assisted selection (MAS). Therefore, precise and easy use of gene-targeted markers would be of significant importance for selection in breeding programs. The present study was undertaken to develop a new marker based on Ty-3 gene sequence that can be used for MAS in TYLCV resistant tomato breeding program. The new developed marker was named ACY. The reliability and accuracy of ACY were evaluated against those of Ty-3 linked marker P6-25 through screening of commercial resistant and susceptible tomato hybrids, and genetic segregation using F2 population derived from a commercial resistant hybrid AG208. With the use of bioinformatics and DNA sequencing analysis tools, deletion of 10 nucleotides was observed in Ty-3 gene sequence for susceptible tomato variety. ACY is a co-dominant indel-based marker that produced clear and strong polymorphic band patterns for resistant plant distinguishing it from its susceptible counterpart. The obtained result correlates with 3:1 segregation ratio of single resistant dominant gene inheritance, which depicted ACY as gene-tag functional marker. This marker is currently in use for screening 968 hybrids varieties and one thousand breeding lines of tomato varieties stocked in Jiangsu Green Port Modern Agriculture Development Company (Green Port). So far, ACY has been used to identify 56 hybrids and 51 breeding lines. These newly detected breeding lines were regarded as potential source of resistance for tomato breeding. This work exploited the sequence of Ty-3 and subsequently contributed to the development of molecular marker ACY to aid phenotypic selection. We thus recommend this marker to breeders, which is suitable for marker-assisted selection in tomato.
C ytoplasmic male sterility (CMS) has been widely used for commercial hybrid seed production in a number of cereal crops such as maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and rice (Perez-Prat and van Lookeren Campagne, 2002). However, large-scale production of hybrids based on a single CMS system could cause disease epidemics. For instance, in 1970 there was an outbreak of Southern corn leaf blight (Helminthosporium maydis Nisikado & Miyake race T) on U.S. maize hybrids produced using Texas-type CMS that carried a mitochondrial gene T-urfl3 with the dual role of causing CMS and disease susceptibility (Levings, 1990). Cytoplasmic diversification for hybrid production has become a priority goal of heterosis breeding especially for monoclinous crops, such as rice, ever since the 1970 incident (Levings, 1990; Dalmacio et al., 1995). Hybrid rice is currently cultivated on more than 16 million ha, which makes up >50% of total rice area in China (Li et al., 2007) and is also being planted commercially in Southern and Southeast Asian countries such as India,
Multilocation and on stations trials were conducted during 2013 and 2014 to evaluate the performance of twelve rice genotypes under three locations; Sakha (Kafer El-Sheikh Governorate), Gemmiza (El-Gharbia Governorate) and Zarzoura (El-Behira Governorate). The experiments were conducted using Randomized Complete Block Design with four replications. Combined analysis of variance among the different locations was done. The results obtained showed highly significant differences among rice genotypes, locations, and genotypes by locations interaction. The rice genotypes recorded the highest values of grain yield at Gemmiza location, surpassing significantly the other two locations. These results indicate that the studied genotypes responded differently to the different environmental conditions suggesting the importance of evaluation of genotypes under different environments in order to identify the best genetic make up for a particular environment. The rice genotypes GZ9523-2-1-1-1, Giza 179 and Sakha 101 recorded the highest values of grain yield under the three locations, of Sakha, Gemmiza and Zarzoura during 2013 and 2014 seasons compared with the other genotypes, indicating that those genotypes have a good adaptation under different environments conditions. Concerning the grain quality characters among the three locations, all characters were not affected significantly in both seasons, but the differences among genotypes were significant. Stem borer infestation was affect by location and genotype while, rice blast infection differed significantly among rice genotypes. The highest values of infection of rice genotypes to stem borer were observed at Gemmiza location compared with the other two locations. Sakha101 was resistance to stem borer while, Giza177, Sakha105, Giza179, GZ9461-4-2-3-1, GZ9577-4-1-1, GZ9626-2-1-1 and GZ9807-6-3-2-1 were moderate resistance. On the other hand, Sakha106, GZ7576-10-3-2-1 and GZ9523-2-1-1-1 were moderate susceptible. However, Giza178 was susceptible to stem borer. Most of rice genotypes under study were resistant to rice blast, except Sakha 101 cultivar, which was highly susceptible under different locations in the two seasons.
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