Impact of pre-storage seed invigoration in ash gourd (benincasa hispida (thunb.) cogn.)

Abstract

A study to elucidate the effect of seed invigoration on viability and quality of seeds in ash gourd variety KAU Local was conducted at College of Horticulture, Vellanikkara, Thrissur, during 2016-2018. The impact of seed invigoration on seed viability and seed quality parameters under ambient (S1) and refrigerated storage (S2) was assessed following a completely randomized design with seven invigoration treatments (I1 to I7) and three replications. Seeds were separately invigorated using CaCl2 (50 m M) for 12h (I1), CaCl2 (50 mM) for 24h (I2), kinetin (10 ppm) for 12h (I3), kinetin (10 ppm) for 24h (I4), KH2PO4 (10-1 M) for 24h (I5), Pseudomonas fluorescens (1x106 cfu.ml-1) for 12h (I6). Untreated seeds (I7) served as control. Both treated and untreated seeds were dried to < 8 per cent moisture content and packed in polythene bags (700 gauge). The seed quality parameters were recorded immediately after treatment and subsequently at monthly intervals for a period of 10 months, while, germination of stored seeds was assessed up to 14 months after storage (MAS). At bimonthly intervals, quantification of lipid peroxidation, sugar and amino acids leached out from the seeds and the seed micro flora infection was also done. Seed quality during storage and seed longevity were found to be significantly influenced by storage environment, invigoration treatment and their interaction throughout the storage period. The results revealed that germination and other seed quality parameters such as germination index, coefficient of velocity of germination, energy of germination, vigour indices I and II, in both treated and untreated seeds decreased progressively over the storage period. However, there was an increase in mean time to germination, time taken for 50 per cent germination, allometric index, electrical conductivity of seed leachate, seed infection per cent, leachate of sugar, amino acid and lipid peroxidation, towards the end of storage period. Germination of seeds stored under the refrigerated storage was lower than that under ambient storage in the initial storage period (upto 3 MAS). Henceforth, refrigerated seeds exhibited significant superior germination than that under ambient storage till the end of storage period (14 MAS). Germination of seeds under refrigeration was retained above 60 per cent (the minimum seed certification standards required for ash gourd) for 13 MAS compared to 5 MAS in ambient stored seeds. The study thus revealed that irrespective of seed invigoration treatments, to prolong seed longevity and maintain seed quality, storing seeds under refrigeration is advantageous over ambient storage. Irrespective of storage environment, priming induced early germination. The seed quality parameters of the invigorated seeds before storage were found to be superior to untreated seeds. The invigorated seeds had also exhibited a germination per cent above 80 at 1 MAS, while, the germination in untreated control (I7) during the corresponding period was below the MSCS. Seeds invigoration with calcium chloride for 12h (I1) and 24h (I2) recorded significantly high germination and other seed quality parameters during the storage period of ten months. Owing to the significant superiority of seeds invigorated with I1 (CaCl2 50mM 12h) and I2 (CaCl2 50mM 24h) with respect to germination in the initial period of storage (up to 4 MAS), superior seed qualities during storage as well as retention of germination above MSCS for 8 MAS, seed invigoration with CaCl2 50mM before storage can be advocated to help retain seed qualities and prolonging seed longevity during storage. The interaction between storage condition and invigoration treatment on germination and other seed indices pointed out that it was most advantageous to treat seeds with CaCl2 50mM for 12h (I1) before storing under ambient conditions. If provision for refrigerated storage is available, bio-priming with Pf 1x10-6 cfu.ml-1 for 12h (S2I6) or priming with CaCl2 50mM for 24h (I2), kinetin 10 ppm for 12h (I3) or kinetin 10 ppm for 24h (I4) or KH2PO4 10-1 M for 24h (I5) would be most advantageous. Analysis of the impact of pre-storage seed invigoration treatment on seed longevity subsequent to retrieval of seeds from refrigerated storage revealed that, irrespective of the storage period under refrigeration, the seeds were found to retain viability above MSCS for a minimum period of one month after retrieval from refrigerated storage. Viability retention of invigorated and untreated seeds during further periods of thawing was unpredictable. It was also evident that none of the treatments could help retain seed viability above MSCS for five months after retrieval from refrigeration. Results also revealed that seed invigoration with CaCl2 50mM 12h (I1) is advantageous, if one or two months of ambient storage after retrieval from cold storage is unavoidable. Hence, considering the impact of storage environment, invigoration treatment and their interaction on seed longevity and quality, as well as their influence on seed longevity during thawing, it can be summarised that seed invigoration with CaCl2 50mM for 12h (I1) or 24h (I2) would be beneficial.