Factors affecting germination and growth of sugarcane transplants.
Transplants are produced and sold in South Africa for the planting of seedcane supply plots (nurseries), commercial fields, and for gap filling. The most important factor constraining the use of transplants is the low germination of single-budded setts (SBS) planted in polystyrene trays. The main aims of this project were to develop practical methods for optimising germination and to control pathogens without adversely affecting germination. Seedcane quality, cane age, storage and treatments using heat, chemicals and fungicides affected germination and growth. Germination of SBS from old seedcane was significantly higher when taken from the top than from the middle and bottom of the stalk. Storage of seedcane for three and eight days after harvest adversely affected germination and growth. Topping of stalks three days before harvest increased germination potential, but results were variable, depending on cane age, cane quality and further treatments. Treatment of SBS at both 50°C for 120 minutes and 52°C for 30 minutes controlled Clavibacter xyli subsp. xyli (C. x. xyli) (the causal organism of ratoon stunting disease) more effectively than treatment of whole setts. After treatment of SBS at 52°C for 30 minutes, germination was greater than that after treatment at 50°C for 120 minutes, and C. x. xyli was eliminated from stalks of six out of seven varieties. Treatment of SBS at 52°C for 10 minutes significantly improved both germination and plant growth. Treatment of SBS for 10 minutes after addition of ethephon to the hot water significantly increased germination compared with the untreated control, but not compared with treatment with hot water alone. After treatment of SBS with fungicides, germination was highest after treatment with Eria® (Novartis), a chemical with two active ingredients, namely carbendazim and difenoconazole. Compared with no treatment and the short hot water treatment, treatment with Eria® in hot water (52°C) significantly improved germination and plant growth in both unsterilised and sterilised medium. Treatment of SBS and drenching of trays with a solution of propamocarb-HCl and benomyl had no effect on germination or growth, indicating the limited role of systemic infections and soilborne pathogens in germination failure. However, germination and growth were significantly increased when the same SBS were also treated with Eria®, suggesting that germination was predominantly increased by the plant growth regulator activities of its active ingredients. When used separately, both difenoconazole and carbendazim significantly increased germination, and difenoconazole significantly increased plant growth. The conclusion drawn from these results is that germination failure of SBS in trays is mainly due to the inappropriate hormonal balance for germination within .the SBS, rather than systemic infections or infection by soilborne pathogens. Therefore, germination and growth can be optimised by using mature, good quality seedcane, and by treatment of SBS with chemicals that adjust the hormonal balance in the bud region to one appropriate for germination.