Breaking tuber dormancy in Helianthus tuberosus L. and interspecific hybrids of Helianthus Annuus L. × Helianthus tuberosus
Tubers of Helianthus tuberosus L. are dormant after production in the late fall until the next spring. In the wild, tuber dormancy is broken after exposure to winter cold, resulting in sprouting and shoot development in the spring when conditions are favorable. The dormancy period typically limits H. tuberosus populations to one growth cycle per year. An efficient method for breaking tuber dormancy is needed to have an additional growth cycle per year in a breeding program, which could take place in winter inthenurseryorthegreenhouse allowingforincreased breedingefficiency.Theobjective of thisresearch was to compare chemicaland cold temperature treatments for artificially breaking tuber dormancy in 12 genotypes of H. tuberosus and interspecific hybrids of Helianthus annuus L. 3 H. tuberosus. Five cold exposures (2, 4, 6, 8, 10 weeks at 2 8C), three plant hormones (ethylene, cytokinin, and gibberellic acid), and one untreated control were examined. Gibberellic acid was the best chemical treatment, initiating plant growthwithin6.5to11.5daysinthemajorityofgenotypestested.Thebestcoldtreatment was exposure to 2 8C for 8 weeks, where plant growth began 63.6 to 67.5 days after treatment initiation. Although longer cold treatments shortened the time to emergence while in the greenhouse, the penalty of the long cold treatment per se was too long to be useful. The gibberellic acid treatment strategy described here may not need further optimization, because it is short enough to allow for two growth cycles of H. tuberosus per year.
Breaking Dormancy and Effects of Shade Level and NPK Fertilizer Rates on Yield of Zingiber zerumbet (L.) Smith (Lempoyang)
Zingiber zerumbet (L.) Smith, known as Lempoyang in Malaysia, belongs to the family Zingiberaceae. Previous studies on Lempoyang mainly focused on the chemical properties and biological activities of the rhizome extracts of this plant. Despite the tremendous demand for the rhizomes of Z. zerumbet, there is a lack of information on cultivation practices and a scarcity of planting materials. By using the pre-soaked technique, the challenges posed by Z. zerumbet dormancy can be overcome, obtaining good quality and uniform planting material throughout the year. Besides that, it is also crucial to determine the optimum shade level and NPK fertilizer rates to obtain a high yield and good quality rhizomes of Lempoyang. Six concentrations of 6-benzylaminopurine (BAP, 0, 50, 100, 150, 200, and 250 mg/L) and ethephon (0, 150, 300, 450, 600, and 750 mg/L) were tested to evaluate their effects on breaking rhizome dormancy. Three different shade levels (full sun, 30%, and 50% shade levels) and four combinations of Nitrogen (N), phosphorus (P), and potassium (K) (NPK) fertilizer at different rates were evaluated to study their effects on plant growth and yield performance. The results showed that BAP at 100 mg/L and ethephon at 300 mg/L performed better than the other compound concentrations tested in promoting the breaking of bud dormancy. A significant interaction effect was observed between shade levels and NPK fertilizer rates in all the growth parameters examined, except for the number of tillers per plant. Plants grown under 30% shade with NPK 4 produced the highest rhizome fresh weight, dry weight, and yield, but plants grown under 50% shade with NPK 4 showed the highest plant height and number of tillers per plant.
Convergent-divergent selection for seed production and forage traits in orchardgrass. III. Correlated responses for forage traits
Most orchardgrass (Dactylis glomerata L.) cultivars are developed in a two-stage selection protocol. Stage 1 involves selection for agronomic traits among spaced plants and Stage 2 involves selecting among a limited number of clones based on their polycross progeny performance, usually in sward plots. The objective of this study was to quantify genetic progress in sward-plot forage yield and related traits of four orchardgrass populations subjected to two cycles of recurrent phenotypic selection for agronomic traits of spaced plants. Selection was conducted at four locations, using either a regional approach (convergent-divergent) or selection for local adaptation at one location. Selection criteria varied among locations, depending on the local environment and each breeder's goals. Convergent-divergent selection led to a 7 and 8% increase in forage yield of the MO2 and WO11 populations, respectively, averaged over all evaluation locations. Local selection did not lead to forage yield improvement for any population. Both selection methods led to decreased rust reaction in at least two of the four populations and later maturity in all four populations. The improvements in forage yield appeared to be due partly to populational buffering among progeny of plants selected at different locations, phenomenon not possible within the local populations because of single-location selection. These results indicate that selection for agronomic traits of spaced plants in orchardgrass can lead to improved sward-plot forage yield across a wide range of environments when multiple-location selection is applied to some germplasms.