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Seed Production of Red Creole Onion (Allium cepa L.) in the Philippines
Dissertation Abstract:
Unvernalized mother bulbs of Red Creole onion did not flower in Los Banos, Laguna. Philip pines. Those vernalized at 5, 10, and 15 oCfor 75 days had 56, 67, and 51 percent flowering, respectively. All vernalization treatments produced seeds. A subsequent field experiment showed that mother bulbs vernalized with daily shifting at 10 and 20ºC had significantly higher degree of flowering than those exposed to a constant temperature (10ºC) treatment.
Planting date affected flowering of Red Creole onion in Los Banos but not in Batac, I locos Norte in Buguias Province, both in the Philippines. Late planting in Los Banos resulted in higher proportion of flowering plants than earlier plantings. The range of flowering was 6-59 percent, 33-39 percent, and 98-99 percent in Los Banos, Batac, and Buguias, respectively. Seed yields were low (4-20 kg/ha) and their planting date were not significa ntly diffe rent in Los Banos and Batac. No seed was harvested in Buguias because of severe disease damage. Germination of locally-produced seeds was generally low ( 13-52%).
Further vernalization of plants in Buguias, pre-conditioning by exposure to warm temperatures (15, 20, or 25ºC) before planti ng, bulb size, or gibberellic acid (GA3) did not improve floweri ng or seed production of verna lized Red Creole onion in Los Banos, but GA3 inhibited the formation of bulbils. Seedlings vernalized in Buguias did not flower.
The following constraints were identified in local onion seed production: 1) in spite of vernali zation, the degree of bolting and flowering and, consequently, seed yields were too low in low elavation areas (Los Banos and Batac); 2) conditions in the high elevation areas (Buguias) were favorable to flowering, but the dry period was too short for seed maturation; and 3) low bee activity contributed to the low seed yields.
Further studies should focus on the following: 1) development of a variety that will show a higher flowering percentage in the low elevation areas, where the dry season is longer; 2) use of temperature combination during the vernalization process; 3) search for a high or mid-elevation area with a longer dry period; 4) use of bee colonies in seed production fields; 6) use of medium size bulbs (approximately 80g) to achieve higher seed yield/plant; and 7) planting of bulbs when the scape length is more than half of the bulb length.