Analysis of inbreeding depression in west coast tall coconut (Cocos nucifera L.)

Abstract

In nature, coconut is a cross pollinated crop which influences the high degree of variability and heterogeneous population. With the intension of developing inbred line in coconut, the programme was initiated in 1924 by selecting the eighteen WCT palms and developed S 1 generation. The S 1 plants were selfed and sibmated to produce the S 2 progenies in 1960 and the seedlings planted at CRS (RARS), in Pilicode with the replicated trial. This served the present experimental material to characterize and analyze inbreeding depression in S 2 palms and to study the effect of selfing (S 3 ) in selfed and sibmated (S 2 ) families of West Coast Tall (WCT). Vegetative, reproductive and nut characters were recorded in S 2 WCT family. The analysis of variance revealed significant differences among the twelve families of six groups of WCT for all the characters studied. The tallest palms were observed in IVS 2 -2 and IAS 2 -2 and on par with the WCT. The shortest palms were recorded from IIS 2 -1 and IIIS 2 -2 but taller than dwarfs. In general the sibmated families were showing more tall stature indicating heterotic behavior. The IAS 2 -1 and IBS 2 -1 showed average number of functional leaves as tall while IIIS 2 -1 had less number of leaves similar to dwarfs. The petiole length was short in IAS 2 -1 and IAS 2 -2 as well as IIIS 2 -1, IVS 2 -2 and VS 2 -1 indicating an advantageous character of high bearing of nuts with less loss. IIS 2 -1 and VS 2 -1 produced more number of female flowers while IAS 2 -1 and IAS 2 -2 produced less number of female flowers. In IIIS 2 -1 and VS 2 -1, the period of female phase similar to WCT. Thickest kernel was noticed in IBS 2 -1 and VS 2 -2 and less thick in IAS 2 -1. More thickness of kernel is tall palm character and thin meat is dwarf palm trait. Inbreeding depression was studied for S 2 nut yield and its attributes. The family IIS 2 -2 and VS 2 -1 expressed positive inbreeding depression for palm height and internodal length, but no inbreeding depression for stem girth. The leaf characteristics also exhibited positive inbreeding depression in S 2 . The WCTpalms in S 2 generation were characterized primarily based on eight characters separately when selfed and sibmated in S 1 for S 2 generation. In selfed the IBS 2 -1 showed tall characters with highest tall, stouter stem, medium functional leaves, and average female flowers, less setting percentage and low yield, medium nut, high oil percent. Semi tall characters in IIIS 2 -1 which recorded semi tall, stouter stem, average functional leaves, and average inflorescence produced, average female flowers, medium setting percentage, high copra and low oil content. Dwarf characters observed in IIS 2 -1 short, thin stem, high functional leaves, more inflorescence, high female flowers, medium setting percentage, nut yield, copra and oil content high. The S 3 seed nut showed that germination percentage was low in all the families (less than 50%) indicating the operation of deleterious effect of inbreeding in S 3 seed nuts. The semi-tall seedlings were more in selfed and talls in sibmated families of S 3 . The percentage of occurrence of stouter collar girth was more in S 3 (IAS 3 -1, IBS 3 -1, IIS 3 -1, IVS 3 -2, IIS 3 -2, IIIS 3 -2 and VS 3 -2). The leaf production was moderate in all the S 3 seedlings of selfed and four sibmated families (IAS 3 -2, IBS 3 -2, IIIS 3 -2 and VS 3 -2). Both the third and fifth leaves , the length, breadth and petiole length showed moderate values. The germination percentage revealed positive inbreeding depression in all the selfed families of 12 families. High inbreeding depression was noticed in IAS 3 -2, IIIS 3 -2, IVS 3 -2, VS 3 -1 and IVS 3 -1 and the lowest in family 1BS 3 -1 and 1AS 3 -1. Seedling height expressed high inbreeding depression in VS 3 -1. Collar girth didn‟t show inbreeding depression in S 3 . It is an important trait correlated with yield. Both positive and negative inbreeding depression was recorded for total number of leaves produced by the seedlings in S 3 generation. The molecular study using the promising inbreds was done using 10 primers. The analysis by the primers signifies that the family IIIS 3 -1 was unique which was noticed by the 5 primers i.e. OPBA 03, OPAW 19, OPAW 15, OPAW 09 and OPAU 02. The specific bands for dwarfs were noticed from almost all theprimers except for the OPAW 09. While the locus specific to tall have noticed from the primer OPBA 03 and OPAU 03. The specificity to the samples has also been noticed from some primers which was the WCT specific (OPAU 03), CGD (OPAW 15 and OPAW 08), IAS 3 -1 (OPAW 12, OPAW 13 and OPAW 08), IBS 3 - 1 (OPAW 19 and OPAU 03) and IIIS 3 -1 (OPAW 19). The coloured types IAS 3 -1 and IBS 3 -1 were highest and observed as on par with the WCT which were evidently proved by the primer OPBA 03 and OPAW 19. Among the primers, highly significant bands between the tall and dwarf was noticed by the OPBA 03 and OPAU 03. It is evident from the studies that the selfing of WCT palms would reduce vigour and possible to develop inbred lines which could be used for the production of hybrids for higher productivity.