Comprehensively evaluating the cold tolerance of pitayagermplasms

To identify the cold-tolerant ability of pitayagermplasms,the tissue cultured seedlings of 9pitayagenotypes were treated under-3℃stress for 48h.The cold injury rate,cold injury index,the physiological and biochemical parameters were investigated under low temperature stress.A comprehensive evaluation of the cold tolerance was carried out with the combination of principal component analysis and subordinate function value analysis.The results showed that the cold injury rate and the cold injury index significantly varied among the tested genotypes.The cold injury rate was closely related with cold injury index.Genotype B7ranked the first in cold tolerance with the cold injury rate and cold injury index of 31.14%and 20.67,respectively.Genotype B ranked the second in cold tolerance with the cold injury rate and cold injury index of 38.40%and 22.10,respectively.Genotype B2,B4and ZY showed the least ability of cold tolerance.The physiological and biochemical parameters are highly diverse among the tested genotypes as exposure to low temperature stress.There was no close correlation between either soluble sugar contents or peroxidase(POD)activities and cold tolerances of pitayagermplasms.There was significant correlation between either superoxide dismutase(SOD)activities,catalase(CAT)activities, POD activities,soluble protein contents,or proline content and malonaldehyde(MDA)content and the cold tolerance,which may be used as a primary indicator for evaluating cold tolerance for this crop.Among the tested genotypes,the order of cold tolerance was B7BZihonglongHonglongguoHongbaoshiHonglongB2B4ZY.