Current Status of Research on Sugarcane Yellow Leaf Syndrome in Southern Africa

In the 1960s, yellowing symptoms in sugarcane were seen throughout East Africa. This was called ‘yellow-wilt’, a condition first described in Tanzania in 1962. The symptoms appear identical to those of Yellow Leaf Syndrome (YLS). In South Africa symptoms of YLS were first observed in 1994 and were conspicuous in varieties CP66/1043, N22 and N26, intermediate in N27 and less conspicuous in NCo376 and N14. Elsewhere symptoms have been linked to the presence of sugarcane yellows phytoplasma (SCYP) and/or sugarcane yellow leaf virus (SCYLV). However, in many instances symptoms are not accompanied by either pathogen. SCYLV was first detected in South Africa in 1997. At that time the virus was largely restricted to the northern regions, being found in some commercial varieties and certain genotypes undergoing selection in Pongola. The source of infection was thought to be varieties imported from the USA, Mauritius or Zimbabwe during the late 1980s. More recently the disease has spread to the south, but is still more prevalent in the northern irrigated areas. A survey of the industry revealed that more than two thirds of varieties grown in the north are infected with SCYLV, and approximately a quarter of varieties grown in the southern areas are infected. While other countries have reported significant yield loss in SCYLV infected cane, the effect of the virus, and of the phytoplasma, on South African varieties is not yet known with certainty. In this communication we discuss advances in the detection of both pathogens, tissue culture for the ‘curing’ of infected material and ‘circumstantial’ evidence indicating that yield loss does occur in South African varieties.