Sorghum Breeding Nursery Management

Key factors include soil uniformity, water and air drainage, direction of slope, wind and light, general soil fertility level, previous insect, disease, weed, and cropping history, rainfall patterns, water holding capacity of the soil, availability of irrigation water, velocity of wind, frequency of storms, and adequate area for the total program objectives. Accessibility of the site from main offices and laboratories, as well as all-season road conditions, must be compatible for frequent and timely completion of critical work with a flexible supply of workers as the work load changes. The design of the field layout should be tailored to considerations allowing maximum use of light by placing rows perpendicular to the sun's path, adequate bordering of plots with 75-100 cm from alley ways, height and maturity differences of adjacent plots, the amount of seed required to plant the plots, and the use of the harvested seed. Yield and sample production for chemical analysis should be in a plot containing a minimum of three rows with yields and samples taken from only the center row. If heights and maturity groups cannot be planted in groups, five or six row plots should be used. Cytoplasmic male sterility is a key tool in sorghum breeding nursery management, allowing for efficient crossing and pollination procedures. The use of cytoplasmic male sterile plants for test crosses is easily accomplished by uniformly bagging the plants with dated bags when the panicle is one-half exerted from the flag leaf. Pollen can be collected by bagging male plants in the late afternoon with ricked bags and carrying collected pollen to receptive female plants the next morning. It is essential that the pollen be handled in dry bags to ensure viability. Genetic male sterility is also utilized in sorghum breeding nursery management to allow random or controlled intercrossing of isolated populations. This results in a minimum amount of record-keeping with assurance of potentially maintaining a maximum of variability. Identification of male sterile plants in isolation plantings at pollinating time and harvesting of only those male sterile plants grown in association with selected male entries assures cross pollination. Selections from subsequent isolation block plantings based on maturity, height, quality, or phenotypic characteristics, as well as disease, insect, and climatic adaptation, permit rapid evaluations for individual plant selections. Proper planting techniques are critical in sorghum breeding nursery management. Overplanting viable seed at a uniform depth of two to three cm in a well-packed seedbed will provide adequate plants which can be thinned to the desired stand count. Stand counts should range from 17 to 22 plants per meter in 75 cm rows, when yields are being evaluated under adequate rainfall or irrigated conditions. Maximum seed yields per plant by increased tiller production and head size would be obtained by space planting individual seeds. Planting success is increased by adequate seed treatment to prevent disease and insect damage to seeds and young seedlings.