Evaluation of hybrids and clonal variants in pineapple(Ananas comosus L.)

Abstract

The present investigation entitled “Evaluation of hybrids and clonal variants in pineapple (Ananas comosus L.)” was conducted during August 2017 to August 2021 at Department of Fruit Science, College of Agriculture, Thrissur, Kerala. The objectives of the research work were to evaluate the somaclonal variants and hybrids of pineapple for yield and quality for identifying novel genotypes and to generate DNA fingerprints of the genotypes using ISSR markers for varietal identification and assessment of genetic resemblance. The plant material for Experiment-I comprised of 75 somaclonal variants derived from the pineapple cultivar Mauritius. They were field planted and evaluated at FCRS. The material for Experiment-II comprised of 25 numbers of Mauritius x Kew and 10 numbers of Kew x Mauritius hybrids which were selected and evaluated at FCRS, by adopting RBD with two replications during the normal season along with the cultivars Mauritius, Kew, and Amritha. For Experiment-III, molecular characterization of 11 superior somaclones along with the parental source was carried out using fifty ISSR markers. Similarly molecular characterization of 10 promising hybrids and three check varieties namely Mauritius, Kew, and Amritha were carried out using fifteen ISSR markers. All the somaclonal variants of Mauritius and their field evaluated hybrids were scored based on the most desirable and undesirable characters. Statistical analysis was performed by using the different selection criteria for somaclones and hybrids. Somaclones were selected by calculating index scores (Singh and Chaudhary,1985) and hybrids were selected based on selection index (Smith, 1937). With relation to this, the scores of individual genotypes were judged and those genotypes which ranked with the highest index values in the selection indices were carried forward for further study. The statistical analysis was performed by using the selection criteria for somaclones using index scores as suggested by Singh and Chaudhary (1985). It was observed that the sum of index values of somaclones which secured rank with the highest index scores within the eleven were identified. Accordingly, eleven somaclones T-4, T-17, T-71, T-47, T-43, T-25, T-22, T-24, T-75, T-10 and T-69 were selected for further molecular characterization. Among the 50 ISSR markers that were used for PCR amplification, only 30 showed polymorphic amplification. The unique amplicons (1-6) and PIC (0.32-0.94) were recorded from ISSR marker profiles. A UPGMA based dendrogram, minimum (0.58) similarity was showed by the parent genotype Mauritius with the somaclonal variants T71 and T-75, indicating the existence of significant genetic variation among these three variants. The selection index developed by Smith (1937) was used to discriminate the genotypes based on selected characters. As per the selection index of Mauritius x Kew hybrids, it was found that the indices have identified the six hybrids. Accordingly, six numbers of Mauritius x Kew hybrids T-1 (H-17), T-7 (H-43), T-8 (H-66), T-14 (H-70), T15 (H-59), and T-24 (H-35) were selected for further molecular characterization. All the 15 ISSR markers that were used for PCR amplification showed polymorphic amplification. The uniqueness of amplicons (1-7) and PIC (0.43-0.93) were recorded. A UPGMA based dendrogram showed that the hybrids H-17, H-35, and H-43 had the high level of Jaccard’s genetic similarity relationship with parent sources Mauritius and Kew, with a similarity coefficient of 0.72. With the selection index of Kew x Mauritius hybrids, it was found that the indices have identified the four hybrids. Accordingly, four hybrids T-9 (H-121), T-2 (H-118), T-4 (H-101), and T-3 (H-115) were selected for further molecular characterization. All the fifteen ISSR markers used for PCR analysis showed polymorphic amplification. The uniqueness of amplicons (1-6) and PIC (0.41-0.81) were recorded for the ISSR primers. A UPGMA based dendrogram showed that the H-115, H-118, and H-121 have registered a high level of Jaccard’s genetic similarity values with parent source Kew and Mauritius, with a genetic similarity coefficient of 0.66. Thus, this study has analyzed 75 somaclones derived from cv. Mauritius, 25 hybrids of Mauritius x Kew, and 10 hybrids of Kew x Mauritius. Based on the selection indices developed, the superior somaclones and hybrids were identified. The identified lines were characterized using the ISSR molecular marker system which had revealed the genetic relativeness among the selected somaclones and the hybrids.