An evaluation of the performance of variety N21 in field trials.

In 1989 variety N21 was released in the rainfed areas of the South African sugar industry as a variety highlyresistant to eldana borer. Its subsequent inclusion in the agronomy variety trials programme has to date produc.ed 32 harvested crops from 18 field trials, the results of WhICh are given m this paper. Comparisons of yield and cane quality, reaction to eldana borer and selected agronomic characteristics are made, relative to NC0376.The yield performance of variety N21 relative to other commercial varieties in seasons of favourable and droughted conditions is discussed. Under favourable rainfall conditions N21 did not perform as well as varieties N12, N16, N19 and NC0376. However, when conditions of stress were experienced both in the presence and absence of eldana, the performance ofN21 was superior to that of other varieties. Introduction In October 1989, N21 was released in the rainfed areas of the sugar industry as a variety highly resistant to eldana borer. This characteristic suggested that the variety would be suitable for use in areas of high eldana risk, particularly where cane might need to be carried over. New sugarcane varieties are recommended for release by the Experiment Station on their sucrose yielding ability, resistance to pests and diseases and other agronomic characteristics. Releasedvarieties and varieties in the pre-release stage are routinely included in the A~ronomy department variety programme for further evaluation, The mam objectives of the agronomy programme are to compare new varieties with currently grown varieties in as many different environmental situations as possible, to determine varietal responses to farm and managerial practices, to provide a continuous assessment of released varieties and to collect information to help in choosing the most profitable sugarcane variety (Inman-Bamber and Stead, 1990). The agronomy variety programme, initiated in 1966, currentlyconsists of over 40 field trials distributed throughout the industry. Results which include N21 have been obtained from 32 harvested crops and 66 sampling occasions from 18 trials conducted in the past three seasons. The results are discussed in this paper. Experiment procedures Field trials were randomised, each trial including four to nine varieties replicated five to eight times. Row spacing ranged from 1,0 m to 1,4 m and plot sizes from five to six rows of 8-10 m long. One row on each side of each plot and o5-1 0 m at the end of each nett row were discarded for g;owth measurements and measurements of yieldat harvest. Cane in each plot was weighed at harvest and a sample of 12-16 stalks taken from each plot for sucrose analysis. At harvest an assessment was made of the level of eldana damage to the crop. A sample of 25-50 stalks was randomly chosen from each plot and records made of the numbers . of joints, damaged joints and eldana per stalk. 28 Yielding ability is determined in field trials in which the new variety is grown under identical conditions to standard varieties. For many years NC0376 constituted more than 70% of sugarcane crushed, and was grown throughout the industry. Whereas NCd376 has been the standard variety since these trials started, varieties N12 and N14 are now included as additional standards in the south and north of the industry respectively. Results and discussion Sucrose content Figure 1 shows the sucrose content of N21 expressed ~s a percentage of that of NC0376. The seasonal pattern IS distinct, with evidence of a sucrose content slightly better early in the season (April) increasing to a mid/late season (September)advantage Ofabout 6%. The mean sucrosecontent of N21 from all trials was 5% (0,75 units) higher than NC0376. In the absence of eldana, the sucrose content of N21 was 3%(0,4units) higher. Results from four trials where levels of eldana in NC0376 ranged from 18to 38 eldana per 100stalks (e/lOO) (mean26 e/lOO), showedthe mean sucrose content ofN21 was 20% (1,8 units) higher. 115,. ----------------. , l, <0 . '6 110 U z . s 105 Q) > . l'll Qi 100 . C Q) C 95 o o Q) VI e 90 o :J VI (\j 85 L. _ . _ . _ . _ . _ . Z 1 2 3 4 5 6 7 8 9 10 11 12