Seed Quality of Soybean (Glycine Max [L.] Merrill) Genotypes under Varying Storage and Priming Methods, Mother Plant Nutrient Profiles and Agro-Ecologies in Kenya
Chirchir, Grace Jepleting
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world. The demand for soybeans in Kenya is high yet production is negligible due to various challenges, one of which is lack of a well-organized soybean seed system. Soybean seed has been known to deteriorate rapidly in the tropics but the rates vary with the environment, initial quality of the seed and genotype. The broad objective of the research was to enhance soybean seed longevity and vigor through manipulation of storage and priming methods, mother plant nutrition and agro-ecology. A socio-economic survey was conducted to evaluate soybean enterprise, seed handling and quality in Meru South - Tharaka Nithi County. A seed storage trial was done to assess the effect of agro-ecology, genotype, seed dressing and storage materials on soybean seed longevity and vigor. Soybean genotypes tested Gazelle and TGx 1740-2F(SB19) were dressed with wood ash and Apron star® and stored in sealed plastic cans and synthetic gunny bags in farmers stores at Kirege (UM II) and Igambatuntu (LM IV) in Meru South. Monitoring of seed quality during 8 months of storage was done by moisture content, germination, electrical conductivity and accelerated ageing tests at Genetic Resource Research Institute Laboratory, Muguga. The effects of osmo and hydro-priming seed invigoration techniques on soybean seed quality and storability of primed seed was assessed. The influence of mother plant nutrition, genotype and agro-ecology on soybean productivity and seed quality was carried out at Muguga (LH3) and Nkoroi in (UM4) during the short rains of October-November 2013; and seed quality analyzed using accelerated ageing and electrical conductivity tests. Soybean farmers survey revealed that soybean was grown mostly by older (>40yrs -79%), small scale (0.9Ha) mixed farmers on small parcels (0.05ha) and producing low yields of about 283 kg ha-1 . Soybean was newly introduced (<4yrs - 89%) crop, grown mainly in the short rains (84%) as a pure crop (77%), with main varieties being Gazelle (82%) and TGx 1740-2F (14%). Due to lack of assured markets, the crop was mainly grown for own use (74%) mostly as composite flours. Due to lack of a certified seed, farmers relied on farm-saved-seed, stored in synthetic gunny bags (89%) for 1-8 months, with viability ranging from 0% in the warmer LM4 to 100% in the cooler UM2. The seed storage study showed that hermetic storage in sealed plastic Jeri cans, seed dressing with wood ash and storage in cooler agro-ecologies (UM2) was found to be effective and low cost seed storage method for enhancing soybean seed viability and vigor. Soybean genotype SB19 had higher viability, longevity and vigor than Gazelle. Priming enhanced seed vigor by reducing seed leachates, but reduced germination. The 24 h priming duration and PEG -1.0 Mpa was the most beneficial treatment for SB19 but not for Gazelle. Primed seed retained high vigor after 8 months of post priming storage than non-primed seed. The manipulation of mother plant nutrition genotype and agro-ecology revealed that soybean grown in cooler LH3 had greater longevity and vigor, but with lower yields than seed grown in the warmer LM4; and TGx1740-2F resisted field weathering than Gazelle. Nitrogen and Phosphorus fertilization had no effect on soybean productivity, but N25 and N25+ P60 enhanced seed longevity, but these effects varied with site and genotype. The study recommends establishment of source of quality seed, streamlining marketing and promoting utilization of soybean to enhance production of the crop. Seed dressing with ash and storage in hermetically sealed plastic cans in the cooler highlands is recommended for better seed quality. In addition seed should be produced with good nutrition, in the cooler highlands for enhanced longevity. Priming is recommended for enhancing vigor of SB19.