## 4 Discussion  
There were many reports of evaluation on pepper germplasm in recent years, which could be used to find the required excellent characters for the breeding of pepper varieties [3; 31; 32; 33]. Morphological characteristics and chemical parameters were two extremely  
Figure 4: Aggregated boosted tree (ABT) reflecting the relative effect of fatty acid concentrations on the concentration and composition of capsaicinoids in pepper fruit. important factors in the study of intraspecific and interspecific genetic diversity and breeding of _Capsicum_[4, 34]. Morphological characteristics include fruit weight, fruit color, fruit length, fruit diameter, etc., and chemical parameters mainly include total phenols, total sugar, titratable acid, ascorbic acid, capsaicinoids, carotenoids, and fatty acids. Fruit morphology played an important role in the study of the variation and classification of pepper. There were various fruit shapes of fruits in different species of chili pepper [35, 36]. The PCA analysis combining morphological characteristics and chemical parameters could divide the three pepper species (74 samples) into three confidence intervals, indicating that PCA analysis could effectively distinguish the three pepper species. The shape of the _C. annuum_ fruit was mostly short horn and _C. frutscens_ species tended to be long finger, and these are inconsistent with previous studies [34, 35]. This may be due to the difference in the genotype and growth environment of the pepper resources studied in this study from those previously studied [4, 37]. The reported literatures demonstrated that _C. annuum_ varied more than the other species in terms of fruit weight, length, and diameter [38, 39, 32] and our work strengthened this argument. However, it was interesting that the longest fruit (S71, _C. annuum_) was longer than those in previous reports [40, 41]. Additionally, the pepper germplasm employed in this study were morphologically differentiated, which was attributed to the variation coefficients of greater than 39%, including fruit weight, length, and diameter (Supplemental Table S2). Early research described a negative correlation between fruit size and capsaicin content [32, 34]. However, a weakly negatively correlation was proved in our work with respect to the morphological indicators (weight, length, and diameter) of _C. annuum_ and capsaicin content (r \(<-0.28\), \(p<0.05\)). The nutrients in peppers mainly include vitamins, carbohydrates, proteins, and capsaicin [4, 14]. Chemical profiles were critical to the overall sensory quality of fruits, such as total soluble solids, soluble sugar, ascorbic acid, or titratable acidity, and could be employed to determine the ultimate application and the preferable market for pepper commercialization [42, 43]. It was well known that total soluble solids, the soluble sugar, ascorbic acid and titratable acidity increase as maturation progresses of pepper fruits [8, 43]. Those compounds investigated in this study were both significant differences that were intra-specific and interspecific of peppers, of which the most significant between species were found in total soluble solids and soluble sugars. It has already been confirmed that fruit color was affected by the composition and concentration of carotenoids (capsanthin, zeaxanthin, \(\beta\) caroten) and anthocyanins (delphinidin), which were very important substances in the peel of pepper [13, 14, 44]. The fruits of _Capsicum_ spp. have various fruit colors, e.g., light green, green, purple, yellow, orange, and red [13, 18, 35]. The red pepper peel was associated with capsanthin content, the yellow with zeaxanthin and beta caroten content, and the purple with anthocyanin, respectively [13, 18]. This study found that some yellow-green and other colored fruits also contained high carotenoid concentrations, whereas some dark green fruits also contained high delphinidin concentrations (Table 1 and Supplementary Table S1).