THE EFFECT OF TWO NEMATODE SPECIES (MELOIDOGYNE JAVANICA AND CRICONEMOIDES XENOPLAX) ON SOUTH AFRICAN-BRED STONE FRUIT ROOTSTOCKS SCREENED UNDER CONTROLLED CONDITIONS

Abstract

The future banning of soil fumigants by 2015 is likely to have a negative impact on the South African stone fruit industry. The industry is currently dependent on a few high-chill imported commercial rootstocks that, in many cases, are not adapted to local soil and climatic conditions. Plant-parasitic nematodes are a severe problem worldwide, with serious economic implications for the fruit industry. Therefore, the continuous improvement and the development of crops with increased resistance or tolerance to pests and diseases, as well as to harsh environmental conditions is of importance. In South Africa the most important plant-parasitic nematodes on stone fruit rootstocks are Criconemoides xenoplax (ring nematode) and Meloidogyne javanica (root-knot nematode). Agricultural Research Council (ARC)-bred stone fruit hybrids were screened for nematode resistance or tolerance under controlled conditions during 2009/10 and 2010/11 at the ARC Infruitec-Nietvoorbij facility at Bien Donne Experimental Farm, Simondium, Western Cape. Screening was done on rooted cuttings in black nursery bags, in a complete randomised block design housed in a greenhouse to evaluate the effect of the two nematode species. Inoculum of C. xenoplax was produced using the peach cultivar ‘Atlas’ as host and for M. javanica the tomato cultivar ‘Moneymaker’. A concentration of 2,000 J2 C. xenoplax in 100 ml soil, and 2,000 eggs M. javanica in water, was added to each plant. After a period of six months, C. xenoplax were extracted from the soil, using a sugar flotation technique and the number of nematodes per 250 g of soil determined. For M. javanica, the soil was washed from the roots and the roots were scored according to a gall index on a scale from 0 to 5. To date, the stone fruit rootstock breeding programme has bred very promising stone fruit rootstocks that are suitable for South African commercial growers and emerging farmers.