The response to reduced light intensity of two contrasting cultivars Puma Sunny (shade intolerant) and Gongzi (shade tolerant) was characterized in terms of plant height, the root/shoot ratio, photosynthetic capacity, and the morphology and ultrastructure of their chloroplasts and phloem companion cells. The initial response to shading of cultivar Puma Sunny plants was to extend their stems, and while the equivalent response of cultivar Gongzi was less marked. Shading depressed the maximum relative electron transport rate (rETR) in both cultivars, and while the efficiency of light capture in cultivar Puma Sunny was compromised by shading, this was not the case for cultivar Gongzi. Low levels of incident light inhibited the formation of starch grains in the chloroplast and increased the volume of interspace between the grana lamellae. In cultivar Puma Sunny, but less so in cultivar Gongzi, the chloroplasts became more slender and the stroma lamellae more swollen. Adjusting chloroplast morphology by developing extra layers of grana lamellae and maintaining the integrity of the phloem companion cells are both adaptations which help make ‘Gongzi’ a more shade-tolerant cultivar.
Shuang Han, Jiafu Jiang, Huiyun Li, Aiping Song, Sumei Chen and Fadi Chen
Shuang Jiang, Haishan An, Xiaoqing Wang, Chunhui Shi, Jun Luo and Yuanwen Teng
Simple sequence repeats (SSRs) are widely used in cultivar identification, genetic relationship analysis, and quantitative trait locus mapping. Currently, the selection of hybrid progeny plants in molecular marker-assisted breeding mostly relies on SSR markers because of their ease of operation. In Pyrus, a large number of SSR markers have been developed previously. The method to identify polymorphic SSRs quickly is still lacking in cultivated as well as wild pear species. We present a large number of polymorphic SSRs identified using a quick in silico approach applied across 30 cultivated and wild accessions from Pyrus species. A total of 49,147 SSR loci were identified in Pyrus, and their genotypes were evaluated by whole-genome resequencing data of 30 Pyrus accessions. The results show that most SSR loci were dinucleotide repeat motifs located in intergenic regions. The genotypes of all SSR loci were revealed in all accessions. A total of 23,209 loci were detected, with more than one genotype in all Pyrus accessions. We selected 702 highly polymorphic SSR loci to characterize the pear accessions with an average polymorphism information content value of 0.67, suggesting that these SSR loci were highly polymorphic. The genetic relationship of Pyrus species in the neighbor-joining (NJ) tree and population structure showed a clear division between the oriental and occidental accessions. The population structure split all oriental pears into two groups: cultivars and wild accessions. These new findings of the polymorphic SSR loci in this study are valuable for selecting appropriate markers in molecular marker-assisted breeding in Pyrus.
Haishan An, Jiajia Meng, Fangjie Xu, Shuang Jiang, Xiaoqing Wang, Chunhui Shi, Boqiang Zhou, Jun Luo and Xueying Zhang
Vegetative propagation by cuttings is a very popular method. However, blueberry propagation using cuttings is still a main factor limiting its expansion because its results can vary according to the blueberry cultivar and environmental factors. This study aimed to evaluate the rooting abilities of hardwood cuttings for six blueberry cultivars (O’Neal, Misty, Diana, Biloxi, Bluebeauty, and Coville) using three different exogenous indole-butyric acid (IBA) concentrations (1000, 2000, and 3000 ppm), and to determine if the cutting position (basal, central, apical) affects rooting performance. A control treatment (0 ppm IBA) was also performed. After 90 days of each treatment, rooting percentage, average root length, and average root number per cutting were assessed and used to calculate rooting index, which is a measure of rooting ability. The rooting percentages of hardwood cuttings differed largely among cultivars and were highest for ‘Bluebeauty’ (68.55%), followed by ‘Biloxi’ (68.01%). The rooting index values of these two cultivars (33.59 and 35.18, respectively) were significantly higher than those of the other four cultivars. The rooting response of blueberry hardwood cuttings to IBA concentrations was quadratic, and 1000 and 2000 ppm IBA were sufficient to express the maximum rooting percentage in most cultivars. The rooting abilities of basal, central, and apical cuttings were similar with treatments with high IBA concentrations. The effects of the cultivar, IBA concentration, and interaction between them on rooting percentage, average root length, and average root number were significant; however, the effects of the cutting position on the rooting percentage and average root length were not. This suggested that the rooting abilities of blueberry hardwood cuttings were significantly influenced by the cultivar and IBA concentration rather than by the cutting position.