Additional file 12: Table S12. Comparation of starch content between accessions carrying heterozygous blocks with high frequency and accessions carrying homozygous blocks in cultivars.
Additional file 17: Table S17. Genomic regions and genes that exhibit a decrease in both heterozygosity and nucleotide diversity during domestication from wild progenitors to cultivars (Top 0.99).
Abstract Background Heterozygous genomes are widespread in outcrossing and clonally propagated crops. However, the variation in heterozygosity underlying key agronomic traits and crop domestication remains largely unknown. Cassava is a staple crop in Africa and other tropical regions and has a highly heterozygous genome. Results We describe a genomic variation map from 388 resequenced genomes of cassava cultivars and wild accessions. We identify 52 loci for 23 agronomic traits through a genome-wide association study. Eighteen allelic variations in heterozygosity for nine candidate genes are significantly associated with seven key agronomic traits. We detect 81 selective sweeps with decreasing heterozygosity and nucleotide diversity, harboring 548 genes, which are enriched in multiple biological processes including growth, development, hormone metabolisms and responses, and immune-related processes. Artificial selection for decreased heterozygosity has contributed to the domestication of the large starchy storage root of cassava. Selection for homozygous GG allele in MeTIR1 during domestication contributes to increased starch content. Selection of homozygous AA allele in MeAHL17 is associated with increased storage root weight and cassava bacterial blight (CBB) susceptibility. We have verified the positive roles of MeTIR1 in increasing starch content and MeAHL17 in resistance to CBB by transient overexpression and silencing analysis. The allelic combinations in MeTIR1 and MeAHL17 may result in high starch content and resistance to CBB. Conclusions This study provides insights into allelic variation in heterozygosity associated with key agronomic traits and cassava domestication. It also offers valuable resources for the improvement of cassava and other highly heterozygous crops.
The chromosome number and karyotype of five native species and one hybrid cultive of Cymbidium was studied by applying fingertip pressing method.The results showed that the C.floribundum Lindl.2n=2x=40=36m+4sm;C.dayanum Rchb.2n=2x=40=36m+4sm;C.bicolor Lindl.subsp.obtusum Du Puy et Cribb 2n=2x=40=40m(4SAT);C.insigne Rolfe 2n=2x=40=2M+36m+2sm;C.eburneum Lindl.2n=2x=40=32m+8sm;C.golden Elf.'Sundust'2n=2x=40=34m+6sm(2SAT).We discussed the relationship and the role in the orchid breeding.
Abstract Bacterial blight (BB) caused by Xanthomonas axonopodis pv. dieffenbachiae ( Xad ) is the most destructive disease of ornamental anthurium. In the present study, foliar resistance of 21 anthurium cultivars were assessed under shaded field and laboratory conditions by injection inoculation of 3 × 10 8 cfu/ml Xad ; disease severity was evaluated using a pretransformed rating scale after symptoms survey. Then six selected cultivars with different resistance levels were evaluated for the induced activities of six defence-related enzymes. The obtained results indicated that the same cultivar shared identical resistance under both conditions, but there was a great variation among the cultivars. Anthurium cv. Pink Champion and Manaka showed the highest resistance, and five other cultivars were highly susceptible. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) in the resistant cultivars increased much faster and reached much higher peak levels than those in susceptible cultivars. Further analyses revealed that the relative resistance index (RRI) significantly positively correlated with the activities of SOD, APX, POD and PAL, but not with catalase (CAT) and polyphenol oxidase (PPO), suggesting that early rapid accumulation of SOD, APX, PAL and POD might be an important mechanism of defence against Xad and could serve as one of the valuable physiological indices for the prediction of BB resistance in anthurium germplasm. Consequently, the identified resistant cultivars and the induced defence enzymes will facilitate the phytopathological research and enhance blight resistance selection in future breeding.
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