Visiting Bitter Gourd (Momordica charantia) from a Breeding Perspective: A Review

Visiting Bitter Gourd (Momordica charantia) from a Breeding Perspective: A Review Hari Kesh1 and Prashant Kaushik2,3* 1Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, 125004 Hisar, India 2Institute of Conservation and Improvement of Valencian Agrodiversity, Polytechnic University of Valencia, 46022 Valencia, Spain 3Nagano University, 1088 Komaki, Ueda, 386-0031 Nagano, Japan * Correspondence: prakau@doctor.upv.es Abstract Bitter gourd is an important vegetable of the family Cucurbitaceae, cultivated mainly in humid and subtropical Asia. Bitter gourd is vegetable with immense health benefits due to the presence of medicinal compounds such as charatin, vicine, and polypeptide-p, which play an essential role in lessening the blood glucose levels. Moreover, bitter gourd fruits are particularly rich in vitamin C, minerals, and carotenes. Here, an effort has been made to critically evaluate the extent of achievements during the enhancement and enactment of bitter gourd breeding programs with the use of latest technologies. Broadening of the genetic base of cultivated bitter groud varieties as a result of enrichment of the existing resources by using the wild species in the breeding programs. Practical seed production technological know-how along with the use of the MS system (male sterility)/chemical-induced sterility procedure is nonetheless vital to cope up with the market demands. Superior yielding bitter gourd hybrids combining early maturity and resistance to biotic and abiotic stresses are regularly needed to cope up with the challenge of bitter gourd production.

Momordica charantia cultivated as food as well as a medicinal plant in Asia, and Africa is the only cultivated species of in Momordica genus (Degner 1947;Walters and Decker-Walters, 1988). However, the recommended region of domestication for bitter gourd lies in eastern Asia especially in Southern China or India (Decker- Walters and Walters 1988; Decker-Walters and Robinson 1997; Marr et al. 2004), Fiji as well as the South Pacific (Smith, 1981) along with southwestern India (Joseph, 2005). The first history claimed the growing of M. charantia in China in 1370 CE (Walters and Yang, 1992). Bitter gourd is abundant in the phenolic acids (Kaushik et al., 2015). Nevertheless, there aren't any archaeological accounts of M. charantia continues to be in China (Yen 1977 The domesticate was believed to arrive from Africa to Brazil with the slave trade then dispersed to Central America (Ames 1939;Marr et al. 2004). Wild sorts of bitter gourds are green to dark blue, spiny, brief and very bitter and abundantly present in Northeastern India (Gaikwad et al., 2008). Based on historical, scientific studies (Chakravarty 1990

Genetic diversity
The importance of genetic diversity in any crop germplasm is well recognized as they provide the basic raw material for selection and hybridization program of plant breeding and crop improvement. The evolution of transgressive segregants in the hybridization program largely depends on the availability of diverse germplasm in the gene pool of a crop. A great level of diversity present in both cultivated and wild relatives of Momordica genus for several important traits. Although interspecific crosses were not successful between these two species (Joseph 2005). However, the formation of bivalents during normal meiotic cycle suggested that these two species are phylogenetically similar (Singh 1990 Ram et al. 2006); Large seed size is recessive to small seed size (Nath and Srivastava 1972); white-coloured epicarp is recessive to eco friendly (Suribabu et al. 1986;Vahab 1989); spiny fruit is dominant over sleek (Vahab 1989); Green fruit colour is actually dominant over yellow (Hu et al., 2002) and is managed by 2 genes (Liu et al., 2005). The bitterness of fruit is a monogenic characteristic, with much more bitterness is actually dominant over less (Suribabu et al., 1986;Dalamu et al. 2012). The monogenic inheritance was described for fruit colour, fruit lustre, fruit area system, and stigma colour, but a digenic form of inheritance was suggested for seed colour (Kole et al. 2012). Nath and Srivastava (1972) discovered immature fruit colour in bitter gourd was managed by one nuclear gene without any cytoplasmic element involved. The light green colours were most likely influenced by incomplete dominance or maybe modifier genes (Hu et al. 2002). The constant perturbation in fruit length indicated its quantitative inheritance and over 4 genes had been reported to be engaged in managing this

Heterosis breeding
Degree of heterosis depends on the genetic divergence between parents involved in the cross, their mode of reproduction, traits to be studied and the plant developmental stage. This hypothesis suggests that heterozygosity at individual loci as leading to heterosis. Heterosis is mainly utilizing dominance variation (Kumar et al., 2020). The exploitation of heterosis is more feasible in bitter gourd due to its cross-pollinated nature. The crucial points for the exploitation of heterosis are the identification of superior and divergent inbred lines, information on the combining ability of inbred lines and production of hybrid based on the pedigree and combining ability of inbred lines. It will be hugely beneficial to the breeder if a correlation could exist between the genetic distances of hybrid parents and the yield obtained from their respective cross or hybrid. Molecular markers can be used for prediction of heterosis based on genetic diversity of parental lines was earlier demonstrated in several other crops, like in rice (Xie et al., 2013). The preferable parameters to satisfy the consumer demands are soft fruits with a smaller number of seeds, minimized ridges, uniform green colour, high vigour, a more significant number of female flowers, good fruit setting and high yield (Al-Mamun et al., 2015). However, consumer preference is varied in region wise.
Light green, medium-long, spindle fruit are preferred in Vietnam, during long cylindrical and smooth fruit and light-green in Thailand. South Asian consumers like small-to-medium size, dark-green, spindle-shaped fruit with spiny exterior surfaces. In Taiwan and India, white fruit is used in soups (Dhillon et al., 2016). A lot of variabilities was noticed for vegetative and fruit figures in bitter gourd. Due to the presence of large variability, monoecious characteristics, convenient and conspicuous flowers along with a substantial selection of seeds per fruit bitter gourd work as a prospective crop for the exploitation of heterosis (Thangamani and Pugalendhi, 2013). As bitter gourd does not show or very negligible inbreeding depression, the homozygous inbred lines developed after 6 to 7 generation of continuous selfing. Before making the crosses between inbred lines directly, information regarding the general and specific combining ability will help the breeder in getting the superior hybrids (Haripriya, 1991). High general combining ability effects for different characteristics may help identify better parents with favourable alleles for different components of yield (Acharya et al., 2019). Thus, a substantial general combining capability of the parents appears to be a dependable criterion for the prediction of certain combining ability (Sidhu and Brar, 1977). In Bitter gourd, heterosis continues to be noticed for days to very first female flowering, fruit per yield and vine per vine (Vahab, 1989), vine measurements, fruit measurements, as well as yield per vine Devadas (1993), fruit fat as well as yield per vine (Richard et al., 1995), vine length, days to first female flowering, fruit length and fruit number Celine and Sirohi (1996), fruit flesh thickness and fruits per vine (Jadhav, 2009) Table 1).

Interspecific Hybridization
The Inter-specific and intra-specific hybridization has an essential role in tracing the genomic relationship and improving crops by transferring desirable agronomic characters and some specific traits such as disease, pests and stress resistance from wild relatives to cultivated ones (Bowely and Taylor, 1987). In Momordica, studies were carried out on inter-specific hybridization to establish phylogenetic relationships (Vahab 1989 Table 2.   Overall, 45,859 protein-coding genes were determined and based on the synteny bitter gourd was determined to be more closely related to watermelon (Citrullus lanatus) as compared to cucumber or melon. Interestingly, it was determined that trypsin-inhibitor and ribosomeinactivating genes were the notable characteristics in the bitter gourd genome (Yilmaz and Further inbreeding or selfing is performed for several generations to produce the uniformity in the inbreds before their crossing to develop them into hybrids. Moreover, there is not any significant inbreeding depression in the bitter gourd; therefore, inbreds are regularly maintained by selfing. Further inbred testing is performed for their combining ability via employing several matting designs Line by Tester analysis, diallel analyses, etc.
It is further based on the obtained information regarding the general and specific combining abilities, most promising parents are chosen for the hybrid production. With the availability of bitter gourd genome and detailed genetic map, the selection for heterosis related alleles can be easily achieved in the bitter gourd improvement program.
Moreover, to exploit heterosis in bitter gourd, it should not be only for yield but in line with the interest of other important traits such as climate change and also a mix of traits like insect pest and disease resistance. In this direction, crop wild relatives (CWR) can play an important role as they are the storehouse of important genes desired for the improvement of yield as well as stress tolerance. Bitter gourd is especially vital to countries like in South East Asia where the population is still poor and can not afford the medications for the treatment of their chronic illness. There is considerable reliance on the plants with therapeutic potential, and bitter gourd has been proved as a cure for many chronic diseases. We hope the use of bitter gourd likewise will increase in the western world and feature some significant research roads which ought to be organized. Failure to generate and provide a qualified amount of hybrid seed, specifically of general public bred hybrids warrants urgent notice.