Malavika Dadlani

This open access edited book is a collection of 21 chapters synthesized from nearly 100 lectures by >70 eminent international and Indian experts.

Seed priming is a commercially used technique for improving seed germination and vigour. It involves imbibition of seeds in water under controlled conditions to initiate early events of germi- nation, followed by drying the seed back to its initial moisture content. This review article summa- rizes the recent information available on the various subcelluar processes associated with priming which lead to seed enhancement. The paper discusses the role of synthesis of specific proteins in re- sponse to priming. The effect of priming on DNA repair, gene expression and synthesis of new mes- sage and protein synthesizing machinery are included. The enhancement in the energy metabolism of the cell by priming and the effect of priming in advancing and synchronizing the stage of the cell cycle are discussed. The article also includes information on the role of priming in specific cases, such as alleviation of dormancy in thermosensitive crops which require ethylene. The relationship between seed longevity and priming and methods to prolong longevity, wherever required after priming and the role of desiccation-related proteins, which accumulate during these treatments are also discussed. An illustration summarizing the information on all the metabolic processes which could possibly contribute towards the enhancement in seed performance achieved by priming is included. The paper identifies areas where information is lacking and potential for more in-depth research exists.

Abstract Seed germination and dormancy are vital components of seed quality; hence, understanding these processes is essential for a sound seed production system. The two processes are closely interrelated and regulated, both by genetic as well as environmental factors. While dormancy provides an inherent mechanism aimed at the survival of the plant species to withstand adverse external conditions by restricting the mature seed from germinating, the ability of the dehydrated seed to remain viable and produce a vigorous seedling upon hydration under favourable conditions is the key to the survival and perpetuation of the plant species. In addition, quality seed is expected to result in timely and uniform germination under favourable field conditions after sowing to establish a healthy crop stand. Therefore, in seed technology, dormancy is not considered a desirable trait in the seed lots used for sowing. Thus, to achieve the highest germination percentage, understanding the factors controlling these two interlinked and contrasting processes is vital. In seed testing and seed trade, knowledge of seed germination and dormancy is needed for a reliable assessment of seed quality and its planting value, and to make right decisions. Though much is yet to be understood, the present status of knowledge on these aspects has made significant advances, especially in genetic control, molecular mechanism, and physiological and environmental factors influencing germination and dormancy. The information compiled in this chapter may help the seed technologists in developing new methods for breaking dormancy and testing germination,

Abstract Dormancy in rice ( Oryza sativa L.) seed is imposed by certain physical and chemical factors associated with its covering structures, i.e.hull and pericarp. The nature of these germination blocks, their mode ofaction, and processes regulating the release of dormancy are not fully understood. Of nine rice cultivars studied, Ching-shi 15, Stejaree 45, PTB10, and Mahsuri are weakly dormant, and Bansphul, Benaful, Kataktara, Dular, and N22 are dormant. Release of seed dormancy in rice by various treatments, oxidative processes and enzymic changes associated with dormancy, and parallelism between natural and artificially imposed dormancy patterns were examined. The influence of the hull in imposing dormancy was stronger and more prolonged than that of the pericarp. Application of GA 3 was effective in inducing germination only in weakly dormant cultivars. Dormancy was completely released in all cultivars by subjecting the seeds to moist heat treatment, by removing the hull and pericarp, and by applying GA 3 after dehulling. Dormant cultivars had higher O 2 uptake rate and peroxidase activity and lower amylase and dehydrogenase activities than the weakly dormant ones. Hull removal substantially decreased peroxidase activity but enhanced amylase and dehydrogenase activities. Nonanoic acid (C 90 ), a short-chain saturated fatty acid (SCSFA), when exogenously applied to non-dormant seeds imposed dormancy. Dry heat treatment or presoaking in 0.01 m KNO 3 or 0.1 m H 2 O 2 was very effective in releasing SCSFA-imposed dormancy. Amylase activity was greatly reduced by treatments with nonanoic acid (C 90 ) or ABA. Considering earlier reports and results of the present study, it is proposed that seed dormancy in rice is regulated both by the presence of SCSFAs and ABA in the hull and the pericarp. The relative significance of these substances in cultivars of tropical and temperate origins and its implications in terms of ecogeographic adaptability are discussed.

Abstract Storage is an essential component of seed programmes, which primarily aims at maintaining the high-quality standards of the seed from harvest till the time of sowing the crop in the next or successive seasons. In addition to this, seeds are also stored for longer durations to maintain stocks for seed trade at national and international levels as per market demands and as a buffer against crop failures in times of natural calamities or other exigencies, to maintain seeds of the parental lines for hybrid seed production in one or more seasons, to conserve active genetic stocks for breeding purposes, and to maintain germplasm for long term use. Seeds of most of the agriculturally important species are categorised as orthodox or desiccation-tolerant. Their longevity increases with decrease in storage temperature and the relative humidity of the storage environment (or seed moisture content). However, notwithstanding the constitutional differences among plant species concerning seed longevity, being a living entity, every seed undergoes deteriorative changes during storage, even in dry stores, primarily in terms of germination and vigour due to physiological deterioration, and changes brought by the presence of the pests and pathogens. A good seed programme aims at maintaining the high planting value of the seed in terms of purity, germination, vigour, and seed health during storage by taking care in seed handling, controlling the temperature and relative humidity of the store (or seed moisture in case of hermetically sealed containers), and following good sanitation practices. Considering that the facilities for conditioned storage may not be accessible and affordable in many situations, alternative solutions may be considered, especially for on-farm seed storage.