Agronomic performance of sugarcane varieties derived from tissue culture (NovaCane®) and conventional seedcane under rainfed conditions.
Shezi, Sbonelo Nicholus.
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The use of tissue culture (TC) plants have been promising for the production of true-to-type, disease free planting material. However, TC plants have been shown to possess an altered phenotype (high tillering and thinner stalks) compared with conventionally propagated sugarcane from setts (hereafter referred to as conventional or Con). Limited information is available for the response of different varieties to the TC process. Additionally, the effects of any altered phenotype in subsequent stages has not been evaluated. Three field experiments were conducted under rainfed conditions at South African Sugarcane Research Institute (SASRI) Mount Edgecombe experiment station to gain insights into these factors. The aim of experiment 1 was to investigate growth and yield differences between the TC and the Con plants for different varieties. Here, a field trial was established as a randomised block design with four replications of four varieties (N12, N31, N41, and N48) planted using three methods: 1) TC derived plants (spaced at either 30 (TC30) or 50 (TC50) cm apart; 2) conventional hot water treated seedcane setts (Con); and 3) single-budded sett derived plants (speedlings) planted 50 cm apart (SP50). The aim of experiment 2 was to investigate the effects of different in vitro procedures on several phenotypic and agronomic characteristics of TC plants of sugarcane. A field trial was established as a randomised block design with four replications consisted of two varieties (N41 and N48) derived through three variations of the in vitro NovaCane® procedure, namely i) the standard procedure, ii) plantlets exposed to CoCl2 (NovaCane® (CoCl2)) and iii) plantlets that underwent a secondary meristem excision process (NovaCane® (secondary)) from in vitro material. The plantlets from all three treatments were planted using two (30 and 50 cm) plant spacings. The aim of experiment 3 was to compare the performance of seedcane obtained from TC (stage 1) and Con when planted at different planting rates. The seedcane for experiment 3 was derived from the corresponding treatments in experiment 1, which were: 1) stalks derived from TC50 and planted at a lower planting rate (TC50 low); 2) stalks derived from TC50 and planted at a higher planting rate (TC50 high); 3) stalks derived from TC30 and planted at a lower planting rate (TC30 low); 4) stalks derived from TC30 and planted at a higher planting rate (TC30 high); and 5) stalks derived from Con and planted at a normal planting rate. Yield and yield component measurements for these experiments were taken at harvest and data were analysed by ANOVA. For experiment 1, there were no significant differences in cane yield, stalk height and stalk mass between propagation methods for all varieties in both crops harvested. For varieties N12 and N31, both TC treatments produced significantly thinner stalks and higher stalk population compared with the Con treatment when averaged across crops. Variety N48 was insensitive to the TC process, indicating that the phenotype of this variety was maintained during the TC process. The TC30 and TC50 treatments did not differ significantly for any parameter in both crops for all varieties, showing that plant spacing did not affect growth. The SP50 treatment produced significantly thicker stalks compared with the TC50 for varieties N12, N31 and N41 in the plant crop. For experiment 2, the plants produced through the NovaCane® (CoCl2) procedure resembled those produced through NovaCane® for all phenotypic and agronomic characteristics in the plant and first ratoon crops. The plants produced through the NovaCane® and the NovaCane® (secondary) procedures differ significantly for stalk population only, with the NovaCane® treatment having significantly lower stalk population compared with the NovaCane® (secondary) treatment for variety N41. Planting at closer (30 cm) or wider (50 cm) spacings did not have an effect on plant growth and to the response of varieties to the in vitro treatments. For experiment 3, crop derived from TC had a significantly higher mean cane yield and TERC compared with the crop derived from the Con. The crop derived from TC had a significantly higher mean stalk population compared with the crop derived from Con. This was observed for varieties N12 and N41 in particular. The crop derived from TC produced significantly thinner and taller stalks compared with the crop derived from Con. The effects of planting rates and TC source (TC30 vs TC50) were not significant for any parameter. Varieties responded differently to the TC process (N48 did not show phenotypic variations). As a result, screening of varieties for phenotypic to TC is recommended to make grower aware of expected changes in the phenotype. This should mitigate the risks of possible poor adoption of varieties based on thin stalks. It is recommended that TC plants be propagated using wider (50 cm) plant spacings, as this is more economical. The lack of differences between in vitro procedures suggests that propagation of new genotypes through standard NovaCane® procedures for commercial release should continue. The seedcane derived from the TC at stage 1 can be used as planting materials for commercial production without any negative effects on productivity in subsequent propagation stages. This is despite persistence of the reduce stalk diameter, higher stalk population phenotype. Lack of differences between the higher and the lower planting rates of TC-derived crops suggests that lower planting rates should be used for economic reasons.