Introduction
Economic and nutritional importance of chilli is because of two important fruit quality attributes viz., pungency and colour. Pungency of chilli is due to the presence of capsaicin. Capsaicin is a crystalline, colourless alkaloid, which imparts hotness to fruits. Capsaicin is also widely used in pharmacological preparations, diverse prophylactic, therapeutic, allopathic and Ayurvedic medicines and food industries (Saleh et al., Reference Saleh, Omer and Teweldemedhin2018).
Fruit colour (red) of chilli is attributed to the presence of carotenoid pigments, mainly capsanthin and capsorubin (Kumar et al., Reference Kumar, Munshi, Joshi and Kaur2003), collectively called as oleoresin. Concentrated oleoresin is added to processed meat and to beverages to impart attractive colour. Hence, it is considered to be a best substitute of synthetic colour used in food and cosmetic industries (Kumar et al., Reference Kumar, Kumar, Singh and Peter2006). Enhancing fruit pungency and colour not only ensures better marketability but also easy acceptance of chilli fruits by consumers and food processing industries. Eliciting reliable information on mode of action of genes involved in the expression of oleoresin and capsaicin content is one of the prerequisites for enhancing the efficiency of breeding chilli for oleoresin and capsaicin content. The objective of the present investigation was to decipher genetics of oleoresin and capsaicin content in inter-species cross of chilli based on the combination of first and second degree statistics.
Experimental
Byadagi Kaddi (BK) (Capsicum annuum L.) known for its high oleoresin which bears long slender fruits and Bhut Jolokia (BJ) (Capsicum chinense Jaq.) regarded as seventh hottest chilli in the world which bears very short stout ovate-shaped fruits constituted the basic material for the study (online Supplementary Table S1). BK (P1) as a seed parent and BJ (P2) as a pollen parent were crossed to develop inter-species F1 hybrid during the 2016 rainy season. The true F1 hybrids were confirmed through the presence of very short stout ovate-shaped fruit traits typical to pollen parent. Being inter-species cross and due to low cross compatibility, only three seeds could be recovered from the cross. Of the three seeds, one seed germinated and survived to maturity and produced a few seeds. After conforming true hybridity, the survived F1 (BK × BJ) plant was selfed to derive F2 and also back-crossed to BK to develop BC1P1 and, to BJ to develop BC1P2 during 2017 summer (Fig. 1).
Procedure describing the development of F1, F2 and back crosses involving Byadagi Kaddi (BK) and Bhut Jolokia (BJ).
Forty-day old seedlings of three segregating generations viz., BC1P1, BC1P2 and F2 were planted in contiguous blocks during 2017 rainy season maintaining a spacing of 0.75 m between rows and 0.4 m between plants within a row. Non-segregating generations P1, P2 and F1 were replicated thrice and planted in randomized block design. The experiment was conducted at the experimental plots of Department of Genetics and Plant Breeding, University of Agricultural sciences (UAS), Bengaluru, India. The recommended crop production practices were followed to raise a healthy crop. Due to poor survivability, only 139 F2, 59 BC1P1 and 33 BC1P2 plants survived to fruit maturity.
Red-riped fruits sampled from each of the 139 F2, 59 BC1P1 and 33 BC1P2 plants and those sampled from five plants chosen at random from P1, P2 and F1 were sun dried. Dried fruits were ground to a fine powder and used for estimating oleoresin and capsaicin contents. Oleoresin was extracted by cold acetone percolation of finely powdered sample of sun-dried fruits and subsequent removal of solvent by evaporation over water bath (online Supplementary Fig. S2). The extracted oleoresin was quantified following a gravimetric method (Ranganna, Reference Ranganna1977) as
$${\rm Oleoresin}\;({\rm \%\ )} = \displaystyle{{W_3-W_2} \over {W_1}} \times 100$$where W 1 = weight of the sample taken, W 2 = weight of the empty porcelain dish and W 3 = weight of the porcelain dish + sample extract after drying. Capsaicin was estimated by a colorimetric method (Sadasivam and Manickam, Reference Sadasivam and Manickam1992) and expressed in per cent.
The average oleoresin and capsaicin contents of six generations were subjected for biometrical genetic analysis. Following weighted least square principle, additive genetic effect [a] and dominance genetic effect [d] and, additive genetic variance [σ 2A] and dominance genetic variance [σ 2D] were estimated (Mather and Jinks, Reference Mather and Jinks1982). All the biometrical genetic analyses were implemented using WINDOSTAT software version 9.
Discussion
Inference based on only first degree statistics based [a] are not advisable, as the dispersion of positive and negative gene effects in the parents may result in different degrees of cancellation of gene effects in the expression of traits under investigation (Mather and Jinks, Reference Mather and Jinks1982). Hence, the magnitude of [a] do not necessarily reflect the magnitude of (σ 2A). Similarly, magnitude of [d] does not necessarily reflect those of (σ 2D). Thus, the inference on mode of actions of genes controlling quantitative traits solely based either on first or second degree statistics are often misleading. Hence, inference based on the combination of first and second degree statistics provides complementary and more comprehensive information on the true nature of genetic control of quantitative traits (Kearsey and Pooni, Reference Kearsey and Pooni1996).
Significant but lower magnitude of [a] coupled with [σ 2A] (Table 1) indicated the possibility of dispersion of increasing and decreasing alleles controlling oleoresin content (%) between parents (Bernardo, Reference Bernardo2010, Reference Bernardo2014). Significant estimate of [d] and non-significant estimate of [σ 2D] (Table 1) suggested presence of low magnitude of dominance in the inheritance of oleoresin content. Higher magnitudes of [a] and [σ 2A] than those of [σ 2D] suggested predominance of genes with additive effects in the inheritance of oleoresin content. Significant but negative estimates of both [a] and [d] suggested that inheritance of capsaicin content was controlled by genes with both additive and dominance effects. However, genes that decrease capsaicin content were more frequent than those that increase it and were dominant. Further, genes with additive effects were predominant as could be inferred from higher magnitude of the estimates of additive effects than those of dominance effects (Table 1). Predominance of additive effect genes were further confirmed by higher magnitude of [σ 2A] than that of [σ 2D]. Thus, both oleoresin and capsaicin contents are controlled by genes with predominantly additive effects. As additive gene effects, are fixable, simple high intense selection for higher oleoresin and capsaicin content in early segregating generations is expected to be effective (Acquaah, Reference Acquaah2012). Perhaps, one or two cycles of bi-parental mating in F2 generation which is expected to enhance additive genetic variability and increase the frequency of genes which control higher expression of oleoresin and capsaicin contents followed by selection is the best strategy to improve them in chilli.
Estimates of additive genetic effects [a] and their variance [σ 2A] and dominant genetic effects [d] and their variance [σ 2D] in the inheritance of fruit quality traits in chilli
*Significant P at 0.05, **significant P at 0.01.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/S1479262119000418
