Intra and interspecific compatibility, morphophysiological and their genetic analysis in eggplant (Solanum melongena L.) grafting for bacterial wilt disease resistance

Solanum melongena (eggplant) is one of the most famous and widely cultivated vegetable crops in the world. However, the yield production of this crop is facing a great challenge worldwide including Malaysia, due to most destructive bacterial wilt disease, caused by Ralstonia solanacearum. This study was therefore, conducted to determine the genetic diversity of 42 eggplant genotypes and screening for bacterial wilt resistance eggplant genotypes (from Bangladesh, China, Malaysia. Nigeria and Thailand) and explored the effects of grafting as a potential eggplant breeding to improve fruit yield and quality traits. Among the genotypes used, 4 varieties are F1 (hybrids), 35 are commercial/cultivated and 3 are wild. The analysis of variance (ANOVA) showed that all the traits under study were highly significant variation among the 42 eggplant genotypes evaluated under open field condition. The MBC32 genotype was observed to have a high yield per hectare and yield per plant, with 39.78 t/ha and 2.98 kg/plant, respectively, followed by MBC72 with 37.51 t/ha and 2.81 kg/plant. The phenotypic coefficient of variation (PCV) values was greater than the genotypic coefficient of variation (GCV) values for all traits under study, thus, showing that the differences observed were not exclusively due to genetics but likewise influenced by environmental factors in the expression of the traits. Fruit weight character showed the highest GCV and PCV values (71.2% and 75.8% respectively). High estimated broad-sense heritability and genetic advance values were determined in yield per hectare, yield per plant, number of fruits per plant, fruit weight, fruit length and fruit diameter, indicating that higher of genetic inheritance and genotype selection based on these traits are effective. The 42 genotypes were grouped into four major clusters based on the morphological traits measured using Unweighted Pair Group Method with Arithmetic Mean (UPGMA) dendrogram. The diversity pattern and other performance of the genotypes MBC32, MBC72, MBC45, MBC41, MBC09 and MBC66 from the group I of cluster analysis may be taken into consideration as better parent for an efficient and effective hybridization programme of eggplant. The pathogenicity test based on disease severity index values at fourth weeks after inoculation indicated that genotypes MBC37, MBC55, MBC64, MBC66, MBC51, MBC51, MBC52 and MBC72 had the highest level of resistance to the virulent Ralstonia solanacearum strain, UPMSE 16. As such, the genotypes were confirmed as an appropriate source for the breeding of bacterial wilt disease resistant varieties and also the candidate for a potential source of resistant rootstock for eggplant grafting. Among the SSR used, the average polymorphic information content was 0.373 and it ranged from 0.365 to 0.375. Dendrogram analysis classified these 42 eggplant genotypes into seven main clusters based on SSR marker. It was revealed that the co-dominant markers such as SSR proved to be high effective tool in discriminating between resistant and susceptible genotypes, and classifying these genotypes based on genetic diversity. The grafted plants with MBC50, MBC51 and MBC52 rootstock have proven a remarkable resistance result against the UPMSE 16 strain. The results showed that interspecific grafted genotypes derived from scions grafted onto wild relative rootstocks were produced higher yield as compared to non-grafted and intra self-grafted genotypes. General, the use of rootstocks resulted in higher total and marketable fruit yield compared to the non-grafted and self-grafted scion plants, respectively. In particular, MBC50 and MBC52 rootstock conferred the highest vigour to the scion, resulting in increasing for total and marketable fruit yield, number of fruits, average fruit weight, and fruit length and diameter. The remarkable compatibility and vigour of the rootstock with scion led to the improvement in total and marketable fruit yield. The result of proximate analysis indicated that eggplant of MBC41 grafted onto MBC50, and MBC44 grafted onto MBC50 had a higher protein content in open field and glasshouse conditions respectively, whereas MBC28 grafted onto MBC50 had higher fat content under both the cropping conditions. There was notable effect of grafting MBC66/MBC50, MBC28/MBC50, MBC41/MBC50 and MBC41/MBC51 on the total soluble solid, fruit firmness, pH and moisture content of the fruits, respectively. Furthermore, the organic chemical compound 2, 2-diphenyl-1-picrylhydrazyl (DPPH) was higher in fruits of MBC09/MBC50, while grafted MBC09/MBC51 had remarkably higher ascorbic acid content. High total flavonoid content was recorded in MBC05/MBC50, whereas the level of total phenolic content was found to be higher in MBC44/MBC51 and MBC44/MBC52. Hence, from this study, the use of ‘MBC50, MBC51 and MBC52’ wild rootstocks for grafting displayed resistant to bacterial wilt, good vigour and high yield attributes as well as extend fruit quality. The development of interspecific new eggplant rootstock genotypes from highly resistant wild eggplant genotype (MBC50, MBC51 and MBC52) with Solanum melongena (MBC37, MBC55, MBC64 and MBC66) as possible substitute to those commonly used Solanum torvun will exhibit high and uniform germination, vigour and strong rooting eggplant genotypes for future grafting programme.

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