Studies on yield and quality by retaining tiller in early shipment sweet corn in Yamanashi

Sweet corn is cultivated under optimal climatic conditions in Yamanashi prefecture. These conditions include a large amount of sunshine during the winter season, and an early rise in air temperature and soil temperature in early spring. The main cultivation method involves a cultivar that flowers early from May to June and using tiller-retaining cultivation. The yield of this cropping type is not significantly high (1.4-1.5 t/ 10a), because the seeding time late is from the beginning of February to the beginning of March using the early flowering variety. It is economically important to harvest early and stably without inducing sterility at the top of the ear or creating a look of sub-flowering, and to produce a large spike of strong sweetness. It is considered that the main factor contributing to low yield is a low level of accumulated photosynthate, which causes a small amount of leaf area on individuals of the early variety, and low temperature and low sunshine during the first half of growth. Thus, the purpose of this study is to develop new cultivar technique for increasing the amount of accumulated photosynthate in a plant, elucidating the order and role of emerging tillers, enlarging leaf area of individuals using a tiller, and increasing the amount of supplemental light. As achievement of the objects, these efforts are expected to result in high quality, stability, and high yields in forcing culture of sweet corn. 1. Order of tiller emerging tillers and basic growth in early flowering sweet corn culture 1) Emergence process of the tiller The early variety 'Honey Buntam 36' that was cultivated over a great area in Yamanashi, was tested. The formation process was investigated. A primordium was formed so that the diameter was 0.2mm after the 15th day from seeding when the number of leaves was 2.3 and the 8th node of the highest node order. It was differentiated to the 8th node when the number of leaves was 5.3 on the 28th day after seeding. The axillary bud of the low node order developed at this time, in comparison with axillary bud of the high node order. It was clarified that the tassels differentiated by the 26th day after seeding when the number of leaves was 4.6 and that the female ear had differentiated by the 35th day after seeding when the number of leaves was 6.5. 2) Cultivation factors that affected the emergence and development of the tiller The cultivation factors that affected the tiller emergence process in an emergence of tiller on plastic tunnel culture were investigated. The first emergence was around the 30th day after seeding. The second tiller emerged after 4-5 days, and the third tiller emerged after more 8-10 days. The number of tillers was highest on the 60th day after seeding. After that, it decreased due to competition between individuals or shading. To relationship cultivar condition with tiller emerging tillers is as follows: (1) Variety As the result of investigation of 5 varieties whose that the maturations differ, the number of emerging tillers was from 2.0 to 2.5 tillers per plant without showing a relationship to early or late flowering. The fresh weight of the early tiller was more heavier than later mature one. (2) Cropping type The difference of cropping type on emerging tillers was 1 or 2 per plant. The number of tillers was low in a plastic greenhouse having a small amount of insulation. The number of tillers was high in plants grown in an open field with a high amount of insulation. (3) Amount of applied fertilizer The number of tiller emerging tillers showed a difference ranging from 1.3 to 1.8 per plant, according to the amount of applied fertilizer (composed of three types: nitrogen, phosphate, potassium). The number of emerging tillers was the lowest in the 2.0 kg/a lot that received the basal amount of fertilizer. The number of emerging tillers increased in the 4.0 kg/a lot with the increase in the amount of applied fertilizer. There was no significant difference at applications of over 4.0 kg/a lot (4) Planting density The number of emerging tillers on each planting density was low at dense planting plot and was high at sparse planting within the extent of planting density from 400 to 600 plant/a. (5) Temperature control on seedling stage As to relationship between the lowest temperature on seeding stage and the number of emerging tillers was high at 0 deg C lot of the lowest temperature, and decreased in the 5 deg C and 10 deg C lots as the temperature became higher. The fresh weight of tiller was the heaviest in the low temperature lot. 3) Basal growth in tiller-retaining cultivation The basal growth was investigated when the early variety was cultivated using tiller- retaining cultivation in single plastic-tunnel culture. The growth stages were determined. The growth process of tiller-retaining cultivation in the early variety was divided into 7 grades from I to VII. The change of outside form and the growth conversion of internal organ were considered to determine the stages. Furthermore, each short periods were separated 3 periods as follows: vegetative growth period, vegetative growth period + reproductive growth period, and reproductive ripening period. (1) The main growth stage of I period (around 8 days from seed to emergence) and II period (around 17 days from emergence to the tassel differential period) were fitted to the vegetative growth period around 25 days from seeding to the tassel differentiation period. The growth speed was quite low during this period. (2) The vegetative growth period + reproductive growth period was around 53 days from the tassel differentiation to the completion of fertilization. The growth stages IV , V and VI were fitted to this period. The growth stage IV is around 21 days from the tassel differentiation period to the elongation of the tiller root. The growth stage V is 17 days from tassel earing to the elongation of the tiller root The growth stage VI is 8 days from tassel earing to the completion of fertilization. It was the period that the vegetative growth and reproductive growth advanced duplicate. (3) The ripening period was around 20 days from fertilization completion to harvest time (the 98th day after seeding). It was fitted to growth stage VII. The length and diameter of the cob reached its maximum during this period, 2. Effect of tiller-retaining cultivation on growth environment and yield The effects of tiller-retaining cultivation, i.e., that in which the tiller is retained in regard to the light conditions in the plant community and regarding the tiller and plant growth, and its contribution to the enlargement of the ear on the main culm were investigated. 1) Effect of tiller-retaining cultivation on plant community and growth It was investigated the effect of tiller-retaining cultivation on plant community and growth. (1) Rate of light transmission in the plant community The mean light transmission in the tiller-retained plot was 34 % in the plastic greenhouse culture, and a mean of 35 % in plastic tunnel culture. These rates were 10 % less than those of the tiller-removed lot that showed means of 46 % and 44 %. The absorption coefficient (K) ranged from 0.55 to 0.61 in the plastic greenhouse culture and plastic tunnel culture, while it ranged from 0.3 to 0.35 in the tiller-retained culture. In other words, the rate of utilized light increased. (2) Amount of growth of individual plant, leaf area, and leaf area index (LAI) The rate of tiller occupying all stock and area of individual reached to "28 %. The average leaf area in tillerretained plot was 7,053 cm/stock and was 2.4 times higher in comparison with the 2,953 cm/stock in the tiller-removing lot. The individual leaf area increased and the LAI reached 2.3 times that of the tillerremoved lot (3) Amount of root, exudation, and sugar content (Brix) of culm The weight of the root on the main culm was mean 33.4 g in the tiller-retained lot in comparison with a mean of 24.6 g in the tiller-removed lot. The root weight including the tiller root increased by 60 % when the tiller was retained. The amount of exudation was a mean of 5.1 /time/plant in the tiller-retained lot and increased in comparison with mean 3.9 /time/plant in the tiller-removed lot. Brix of the culm increased in the tiller-retained lot in comparison with the tiller-removed lot 2) Effects of tiller function on plant quality and the enlargement of female flowering The fresh weight was 164 g and the number of grains was 12 per ear in plants in which the female flowers of that all leaves of the tiller and main culm were cut off after the completion of fertilization. It was recognized that the number of grains was 337 when all the leaves of the main culm were removed and the tiller leaves were left. This showed that the tiller contributed to the enlargement of the main culm in female plants, because the ear weight increased in proportion to the number of tillers. 3. The distribution of photosynthate between the main culm and tiller as determined using relabeled isotope 1) The movement of Photosynthate between main shoot and tiller in sweet corn (1) Distribution of I3C -labeled photosynthate when applied to the main culm. It was carried out the movement of photosynthate between culm and tiller using 13C -labeled isotope. The photosynthate was stored in the main culm and was not distributed to tiller after 24 hours when I3Clabeled photosynthate was applied to main culm during the ear enlargement period. The rate of distribution to each organ on the main culm was 65 % in the ear, 22 % in the stem, 3 % in the tassel, and 11 % in the leaf. It was not distributed to root entirely. (2) Distribution of 13C -labeled photosynthate applied to the tiller from the tiller to the main culm Ninety-one percent of the photosynthate was stored in the tiller, and 9 % was distributed to main culm after 24 hours when 13C -labeled photosynthate was applied to tiller during the ear enlargement period. The photosynthate in the main culm was distributed equally to the root, ear, and stem. The amount of photosynthate stored in the tiller was distributed in the assimlatory leaves at 11 %, 68 % in the stem, 9 % in the tassel, and 3 % in the root. High concentrations of 13C - labeled photosynthate existed in the subterranean stem and tiller stem indicating free sucrose, glucouse, and fructose and so on. 2) Distribution of 13C -labeled photosynthate assimilated on tiller leaves The time-course of the movement of the movement of photosynthate was observed as it moved from the immature tiller to the mail culm and from the mature tiller to the main culm. Twenty-seven percent of the photosynthate had moved to the main clum after 24 hours when 13C was applied to the immature tiller. The main part of the main clum containing the photosynthate was the root near the proximal tiller and was slightly distributed to the ear. The photosynthate began to move to the main clum just after anabolism of the mature tiller, with 47 % has been distributed after 2 days. The distribution to the main culm was mostly completed after 5 days. The distribution was 58 % in the main culm, that in the ear was 46 %, that in the stem was 8%, and that in the root was 4 %. The photosynthate was not distributed to the main culm leaves and the tassel did not show complete distribution. Fifty-two percent of the photosynthate was taken into the tiller just before the silking stage survived in the main culm. It was found in the largest amount in ear of the main culm. Most of the photosynthate in the immature tiller was found in the root of the main culm, while that of the mature tiller was found in the ear of the main culm. 4. Effect of tiller retaining-culture under differential environment on the growth and yield of early flowering sweet corn 1) Effect of tiller-retaining culture under differential condition of raising seedling on growth and yield Seedlings were raised in the optimal period and temperature in order to shorten the harvest time in the tiller-retained culture. The amount of growth and weight of the ear decreased and rate of sterility at the tip of ear increased when the seedling period increased in comparison with a direct sowing culture. The period necessary to produce an ear in this culture in relation to direct sowing culture, was reduced by 20 days in the plastic greenhouse culture and 15 days in the plastic-tunnel culture. In this case, the harvest period was lengthened from 13 to 15 days by raising seedlings by both cropping type. The optimal temperature for raising seedlings was 5 deg C. 2) Effect of tiller-retaining culture on growth and yield in relation to differential cropping type, variety, planting density, amount of applied fertilizer, and soil water conditions. The effect of tiller-retaining culture was investigated in regard to the culture environment (cropping type, variety, planting density, amount of applied fertilizer and soil water). The amount of growth increased twofold using the tiller-retaining culture in both cropping types and average ear weight increased from 9 to 17 %, while sterility at the tip of the ear strongly decreased in comparison with the tiller-removed culture. Ear enlargement using tiller-retaining culture showed varietal differentiation. The early flowering variety whose plant height is smaller and number of leaves is smaller showed a high degree of enlargement. Effect of enlargement was recognized until 700 ears /a on each plant density. The amount of growth and leaf area increased dramatically using tiller-retaining culture, with yield being especially increased under dense planting. Effect of each amount of applied fertilizer was not much, even the increase of amount of applied fertilizer. The optimal of soil moisture in the tiller-retaining culture increased leaf area and root size. Thus, it was necessary for high quality and high yield in tiller-retaining culture that optimal moisture be maintained from the silking stage to maturity. 5. Effect of tiller-retaining culture of early flowering sweet corn under different culture environments on sterility at the ear tip Sterility at the tip of ear increased when leaf area and the amount of individual growth was decreased due to soil dryness and low hours of sunshine during the middle and later period (from the middle of May to the end of June). Sterility at the tip showed great varietal differentiation and could not be decreased using artificial pollination. Thus, it was clarified that sterility at the tip constituted a ripening obstacle due to the lack of photosynthate.