Cassava has been grown in Thailand for many decades; the crop occupied 7.7 million rai (1.23 million ha) in 1997. Most of the planting area is in the Northeast with an average fresh root yield of 2.35 t/rai (14.7 t/ha). Many varieties have been released and are now recommended for growing all over the country. However, it is known that genotype by environment interaction plays an important role in yielding ability. Thus, more specific genotypes for particular cassava area need to be identified, especially for the northeastern part of the country. Rayong Field Crops Research Centre, which is responsible for conducting research and development of cassava, has developed a new cassava variety, Rayong 72 (CMR 33-57-81). It was derived from the cross between Rayong 1 (with a good adaptability and plant characters) and Rayong 5 (with high fresh root yield and starch yield) in 1990, and clonal selections and evaluationed were subsequently made. It was tested in the Preliminary Yield Trial in 1992 and produced a high fresh root yield and high starch yield compared to Rayong 1, a recommended variety (Table 1). Rayong 72 or CMR 33-57-81 was selected for further testing in three more locations in Standard Yield Trial in 1993. Results were very promising (Table 2). After this the clone was tested in Regional Yield Trial in 15 more locations to compare with other recommended varieties, such as Rayong 5, Rayong 90 and kasetsart 50. The results are shown in Table 3.

The results show that CMR 33-57-81 had the highest fresh and dry root yields with a moderate starch and root dry matter content compared with other recommended varieties. CMR 33-57-81 was finally tested in farmers’ fields in on-farm trials conducted in 1996-1998 at 42 locations across the country, especially in the Northeast. Results are shown in Table 4.

Results confirmed that CMR 33-57-81 gave the highest fresh root yield with a moderate starch content. It performed, particularly well in the Northeast. From the above mention results, the Department of agriculture has released CMR 33-57-81 as an approved variety, called Rayong 72, and has recommended it for growing mainly in the Northeast.