Mapping quantitative trait loci (QTL) associated with flavonoid in tomato

The flavonoids are a remarkable group of plant metabolites. These are the only secondary metabolites which have been credited with so many diverse essential functions in growth and development of the plant. Anthocyanins are one of the significant components of flavonoid in a plant system. They play a significant role in plant resistances to biotic and abiotic stress. Their bioavailability and biological activities in humans appear to be strongly influenced by their chemical nature. A variety of biological activities possessed by flavonoids include antiallergic, antiinflammatory, antiviral, antiproliferative, and anticarcinogenic activities. Anthocyanins are getting more attention because of their strong antioxidant activity.

Cultivated tomatoes (Solanum lycopersicum L.) do not produce anthocyanin in the fruit, and this trait has been introgressed from wild varieties of tomato. Fruit with the genes Anthocyanin fruit (Aft), Aubergine (Abg) and atroviolaceum (atv) produce varying degree of anthocyanin which is restricted to epidermis layer only and is responsible for imparting purple color. However, no detailed inheritance analysis has been performed for anthocyanin content A backcross population (BC1) was developed from NC74 CAP (2009) (purple) x Ailsa Craig (green) crossings which were grown at Mountain Horticultural Crops Research & Extension Center (MHCREC), Mills River, North Carolina in summer 2017 and BC1S1 population at Mountain Research Station, Waynesville, NC in summer 2018. In 2017, 250 different BC1 genotypes were grown along with the parents in Completely Randomized Design (CRD), and their anthocyanins content were analyzed through high-performance liquid chromatography (HPLC) method. Anthocyanin content in NC74 CAP (2009) and Ailsa Craig was 15.51 and 7 nmole/gfw, respectively. Population mean of anthocyanin was 12 nmole/gfw ranging from 0 to84.31 nmole/gfw. Based on the anthocyanin content, these genotypes were divided into three different groups; low, medium and high. Some progenies fall outside the range of parents, suggesting that there was transgressive segregation, which is one of the characteristics of a quantitative trait. For QTL analysis, we adopted QTL-seq approach and identified four QTL on chromosome 1, 2 and 4.

In order to assess the role of anthocyanins against early blight (EB) in tomato, 32 genotypes of three varying degree of anthocyanin content; 12, 12 and 8 genotypes from high, medium and low anthocyanin level group, incorporating NC1CELBR as negative control and NC84173 as positive control was examined in CRD in laboratory environment. Similarly, 250 BC1S1 genotypes including those 32 genotypes and control lines were tested in MRS, Waynesville, NC in Randomized Complete Block Design (RCBD). Spores of Alternaria linariae in the concentration of ~105 spores/ml was inoculated in experimental genoytpes both in the field and laboratory. The disease was scored using Horsfall-Barratt score. Anthocyanins were found to be insignificant against early blight in tomato suggesting other phenolics like flavonols to be included for carrying out further similar experiments.

Similarly, in order to find out the role of anthocyanins against heat stress in tomato, same 32 genotypes as used for assessing EB resistance, along with Sun leaper as negative control and NC84173 as a positive control was examined in CRD in the greenhouse environment in MHCREC, Mills River, NC. Day/night temperature was set at 35/250C. Heat sensitive structures, mainly reproductive structures such as number of flowers, number of fruits, anther length, style length and style protrusion were analyzed. These analyses revealed the non-significant role of anthocyanins against heat stress in our experiment. In a further similar experiment, we suggest conducting it in strictly controlled environment.

Thus, the evaluation of the role of anthocyanins to circumvent early blight (Alternaria linariae) and heat stress in tomato were found to be ineffective.

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