Evaluation And Genetic Diversity Analysis Of Capsicum Varieties Collected From Southwest China

The Capsicum genus is characterized by variety resources due to their wide adapta’bility,wide cultivation,and long domestication history.For genetic improvement of pepper cultivars,it is important to systematically investigate and evaluate their agronomic traits.In this study,I thoroughly surveyed 34 traits from 150 variety materials collected previously from southwest china,including morphologic traits e.g.fruit shape and plant type,nutritional quality e.g.vitamin C,capsaicinoids and capsorubin and plant physiological traits e.g.maturity and photosynthetic characteristics.Moreover,I surveyed the resistance of 30 materials to Phytophthora capsici by using spores to infect hydroponic plants and separated leaves.At last,36 SSR makers showing good polymorphism screened from 100 SSR markers were used to identify the genetic diversity of the peppers.These above studies provide us better understanding about their phenotypic traits and genetic structure as well as necessary information to utilize them in cultivar genetic improvement in the future.The results are detailed as the followings:1.I surveyed 34 important traits of the peppers.As a result,green ripe fruit color and fruit shape show the richest diversity among the 24 quality traits.Nine and 13 phenotypes were observed for these two traits,respectively.For the 11 quantitative traits,the coefficient of variation(C.V.)ranges from 21.19%to 62.75%and the average C.V.value is 41.29%.The trait of fruit weight shows the richest diversity with the C.V.value to be 62.75%,while plant height shows the least diversity with the C.V.value to be 21.19%.Principal component analysis was performed.As a result,the first 12 factors concerning leaf size,plant type,maturity,color transfer consistency,fruit weight,fruit surface,stalk length,stem hair,flower stalk status,style color were obtained with the cumulative variance contribution rate to be 85.85%.The cluster analysis of 150 materials based on the surveyed botanical characters indicates the peppers can be divided into five groups.The first group had 58 members and they often show finger-shaped or linear fruits and green leaves.The second groups had 37 members.In this group,Yangjiaojiao(29.7%)and Niujiaojiao(45.9%)are the most ones and they often show wrinkled leaves and fruit surface,no fruit shoulder and edge.The third group had 20 members.Their fruit shape was horns or claw-shaped.Their leaf edge is wavy and style length is longer than the stamens.The fourth group had 12 members.They are often bell pepper,with no-hair leaves and flat calyx persistent.The fifth had 23 members.They often have cone-shaped fruit,white corollas and styles.2.Three nutritional and important commercial traits were investigated.The vitamin C content ranges 53.97-226.37 mg/100g and the coefficient of variation was 24.59%.I screen out 17 varieties with high content of vitamin C(>180mg/100g).They were mainly short cone pepper or short finger pepper.The content of capsaicin ranges 0.001%-0.119%with highest in Chaotianjao pepper and lowest in bell pepper.The surveyed pepper can be divided into 3 groups according to their pungency:hot(5materials),middle hot(50 materials),and less hot(95 materials).Fruit color determined by capsanthin content has special meaning for commercial quality.The content of Vc and capsaicin affected by environmental factors significantly;compared with the Chengdu plain,Vc in peppers from south Sichuan Panzhihua and Xichang increased by 46.81%,capsaicin content decreased by 78.89%.The maximum valueof the red degree of pepper fruit is 7.78,the minimum is 0.73,and the coefficient of variation is 47.48%.No pepper containing high content of capsanthin was screened.3.Maturity and photosynthetic characteristics were investigated.The peppers can be divided into 5 groups based on maturity day.Plants of extreme early(<31d),early(31-35d),normal(36-50d),late(51-55d),and extreme late(>55d)take account of 4.00%,12.00%,72.67%,4.67%,and 6.66%,respectively.The six extreme plants are ’CP25’,’CP44’,’CP61’,’CP91’,’CP119’,and ’CP120’,The photosynthetic parameters were determined by Li-COR6400XTR portable photosynthesis apparatus,and the light response curve was fitted according to the non-orthogonal hyperbolic model.The coefficients of variation of light compensation point(LCP),light saturation point(LSP),apparent quantum yield(AQY),dark respiration(Rday)and maximum photosynthetic rate(Amax)were 41.51%,23.82%,16.44%,51.33%and 29.64%respectively.And the maximum apparent quantum yield(AQY)and maximum photosynthetic rate(Amax)were 0.069 and 33.363 μmol·CO2·m-2·s-1,respectively.There are 13 materials showing high photosynthetic rate(>20.000 μmol·CO2·m-2·s-1)and 11 materials showing high light utilization effect(AQY>0.050)and therefore tolerance to week light condition.4.Investigation of resistance to Phytophthora capsici.According to the field performance,a total of 30 suspected resistant materials were inoculated with Phytophthora capsici.By method of vitro leaf inoculation,17 materials were found to produce significant water-soaked stains and 13 materials were resistant.By method of hydroponic plants infection,I identified 6 middle resistant materials,and 1 high resistant material.Together these two results,pepper numbered ’MP128’ is high resistant material.5.The genetic relationship between pepper and genetic diversity was detected by SSR marker.A total of 36 pairs of stable polymorphism SSR markers were screened from 100 primer pairs.And 153 alleles were detected,each pair of which detected 2 to 10 alleles,with an average of 4.25 alleles per locus.The average of allele frequency,gene type number,allele number,gene diversity index,heterozygosity and polymorphism of the 36 SSR markers were 0.73,5.81,4.25,0.38,0.33 and 0.34 respectively.The maximum value of the genetic diversity,heterozygosity and polymorphism information contents were 0.80,0.97 and 0.78,respectively,which indicated that these 150 pepper materials had a certain heterozygosity,and the genetic basis was broad.Based on 36 pairs of polymorphic SSR markers,UPGMA was used to cluster 150 pepper materials.At the genetic distance of 0.24 these materials were divided into four categories.The first category had only one material ’MP94’.The second category had only one material ’M13100’.The third category has 144 materials and is the biggest group.The fourth category has 4 materials:’CP21’、’CP12’,’CP143’and’MP46’.