Incidence, geographical distribution and genetic diversity of sugarcane striate virus in Saccharum species in China

A novel virus of the genus Mastrevirus, family Geminivirdae, was recently reported in sugarcane germplasm collections in Florida, Guadeloupe and Réunion, and was named sugarcane striate virus (SStrV). Although the full-length sequence of a SStrV isolate from China was obtained in 2015, the incidence, geographical distribution, and genetic diversity of this virus remained unclear. A single leaf sample from 2,368 sugarcane plants from main sugarcane producing regions of China and germplasm collections were tested for SStrV by polymerase chain reaction (PCR). Average virus incidence was 25.1% for field collected samples and SStrV was detected in most Saccharum species and two sugarcane-related species with the highest incidence in S. officinarum (44.1%) followed by Saccharum spp. local varieties (33.3%) grown for chewing cane for a long time. The virus incidence was much lower (6.8%) in modern commercial cultivars (Saccharum spp. hybrids). Phylogenetic trees based on full-length genomes of 157 SStrV isolates revealed that Chinese isolates comprised strains A and B, but not C and D that were reported in Florida, USA. SStrV strain A was the most prominent (98.7%) and widespread strain in China and was further divided into eight sub-groups. Almost half (45.6%) of the SStrV-positive samples from S. officinarum and Saccharum spp. local varieties were co-infected with sugarcane mosaic disease viruses or sugarcane yellow leaf virus. Interestingly, most of the plants infected by strain A of SStrV were asymptomatic. SStrV appears to be widespread in China, and its influence on chewing cane deserves further investigation.

Estimation of genetic diversity among sugarcane (Saccharum species complex) clones

he experimental materials consisted of 36 sugarcane clones including two checks (Co Pant 97222 and Co Pant 3220). Analysis of variance revealed significant differences among all the clones for all the traits under study namely no. of millable canes, cane height, single cane weight, juice sucrose percent , purity percent , cane yield and CCS yield except cane thickness, juice brix and juice extraction percent. The divergence studies through Mahalanobis D2 statistics grouped the 36 genotypes into eleven clusters. The maximum numbers of genotypes (21) were grouped in clusterI and the lowest (1) in cluster VI,VII,VIII,IX,X and XI. Members of cluster VII and XI (46.48) were found to be genetically most diverse on the basis of their inter cluster difference as opposite to clusters I and II (10.77) which are closely related. Cane height contributed maximum (15.397%) towards genetic divergence followed by Single cane weight (14.762%) and no. of millable cane (13.016%). These characters were considered to be most important for the genetic diversity. Lowest contribution was made by juice purity percent (4.286%) followed by Cane thickness(7.301%),Juice extraction percent (7.619%). Genetic diversity is important for sustainable production since greater losses of characteristics in any population limits its chances of survival. Little to no genetic diversity makes crops extremely susceptible to widespread biotic and abiotic stresses. Genetic diversity can be assessed by Mahalanobis D2 statistic, which is a morphometric method and a powerful tool in quantifying the degree of divergence at genotypic level.