Identification and diversity analysis of interspecific citrus rootstock hybrids with combination of morphological traits and microsatellite markers

Abstract

Rough lemon is indigenous and has wide adaptability in Indian citriculture. Rough lemon and Volkamer lemon are comparable in horticultural performance and their resistance against biotic and abiotic stresses are almost similar but Volkamer lemon has better adaptability in different agroclimatic conditions. To improve Volkamer lemon hybridization has been attempted with Kinkoji (citrus greening tolerance), Swingle citrumelo (Phytophthora resistance), and Cleopatra (salinity tolerance). Polyembryony in Volkamer lemon and absence of the heritable morphological markers (Cleopatra) are limiting factors for hybrid identification and morphological characters are not being segregated in Kinkoji and Swingle citrumelo at early stage, then molecular markers are employed for detection of putative zygotic seedlings. We performed hybridization between Volkamer lemon (♀), Kinkoji (B cross) (58 F₁) (♂), Swingle citrumelo (D cross) (71 F₁) (♂), Cleopatra (N cross) (83 F₁) (♂) and discriminate the hybrids by using 25 SSR markers. The fifteen markers were found efficient for hybrid identification (> 71% hybrids detected). CCSME23 (88.21%) marker has detected 187 hybrids in all crosses thereafter, 184 hybrids detected each by HvSSRCS-2, HvSSRCS-135, HvSSRCS-237, HvSSRCM-92 and HvSSRCM-466 with 86.79%. A total of 44 qualitative and 18 quantitative characters were analysed. Fifteen qualitative and six quantitative characters were found significant variability in leaf, spine, branch, and stem. Sufficient amount of genetic variability was detected through phylogenetic analysis and population structure analysis showed two subpopulations in B and N cross but in D cross five subpopulations were detected. After primary screening, nine F₁ hybrids for citrus greening tolerance and twelve F₁ hybrids for Phytophthora tolerance were identified. The newly developed F₁ hybrids exhibited phenotypic and genetic diversity along with disease tolerance. These potential hybrids may be recommended for commercial citriculture after thorough horticultural evaluation.