The Effects of Tagetes Spp. on Meloidogyne Javanica in Southern Rhodesia 1) By

THE EFFECTS OF TAGETES SPP. ON MELOIDOGYNE JAVANICA IN SOUTHERN RHODESIA 1) BY

R. A. C. DAULTON AND R. F. CURTIS Nematology Department, Tobacco Research Board of Rhodesia and Nyasaland, Salisbury, S. Rho- desia, and Department of Chemistry, University College of Swansea, Singleton Park, Swansea, Wales, respectively Tagetes erecta, T. patula and T. minuta, when grown in M. javanica infested soil for 42 to 70 days in pots, reduce the nematode populations to low levels. T. minuta, a weed which grows vigorously in Rhodesia, has high levels of a-terthienyl in its roots but this compound, at dosages as high as 200 parts per million, when mixed in infested soil does not control M. javanica. Root-knot larvae fail to penetrate the roots of marigolds in any appreciable numbers and those that enter do not develop beyond the infective second stage larval form.

Results of studies by Oostenbrink, Kuiper & s'Jacob (1957) indicated that populations of four Pratylench¡ls species and of TylencborbyncbaJ dubius were greatly reduced in soil after growing marigolds for one season. The reduction in population of P. pezaetv???a.rwas to about one-tenth of the level of that after other crops and fallow; yields of roses and other susceptible crops following Tagetes were greatly increased. Occasional nematodes entered the marigold roots but failed to develop and reproduce. A possible explanation for the reduction of eelworm populations by T'agete.r spp. became available when Uhlenbroek & Bijloo (1958) found that varieties of the African marigold (T. erecla ) contained nematicidal principles. One of these was a-terthienyl, a powerful nematicide, which had earlier been shown to be present in aerial parts of Tagetes spp. by Zechmeis- ter & Sease (1947). In a later study, Oostenbrink (1960) reported that T'agete.r patula was also effective against Meloidogyne hrlpla: the population in the soil was reduced significantly in comparison to all other crops. T'agete.r niinuta is an abundant weed in most parts of S. Rhodesia and especially on the light sandy tobacco growing soils. M. javanica is by far the predominant species of the root-knot nematodes present in Rhodesian soils and is the cause of large scale crop losses annually. Experiments (started in 1961 ) were made to determine (1) the effect of T. erecta, T', patula and T'. minuta on M. javanica populations in soil: (2 ) the nematicidal activity of a-terthienyl in root-knot infested soil: and (3) the rate of invasion into, and the development of M. javanica larvae in, roots of T'dgete.r spp.

1) Research Paper No. 58, Tobacco Research Board, of Rhodesia and Nyasaland, Salisbury, S. Rhodesia. 358

MATERIALS AND METHODS

Large quantities of inoculum were built up from single egg-mass cultures of M. javanica on Lycopersicon eJculentum Mill. var. Rutgers grown in steamed sterilized soil. Inoculum consisted of egg and larval suspensions prepared by maceration and sieving (Sasser, 1954). Before filling 15-cm pots in sixfold replication, the inoculum was added to steamed soil, sufficient for an entire experiment, and mixed to ensure uniform distribution. The soil in all tests was prepared by sieving and mixing two parts of steamed coarse sand and three parts of steamed sandy loam. Seedlings of Tagete.i- spp. and tomato were established for 14 days in thumb pots after germination in flats of steamed soil. After 35 days the tomatoes were carefully washed out and examined. Root-knot galling was expressed in root-knot index values as described by Daulton & Nusbaum (1961). All experiments were made in glasshouses with temperatures ranging from 22.2° to 26.7° C.

RESULTS The first series of experiments compared the effect of T. ei-ecia and T'. patula on Af. javanica in infested soil, with ( I ) tomato, which is a good root-knot host, and (2) fallow where the infested soil was not subjected to any plant treatment prior to bioassay by test plants for 35 days. TABLE I Root-knot infection indices of indicator plants from soil in rr?hich Tagetes erecta, T. patula and tomato had been grown for 28, 42, 56 and 70 day.r. Results are the mean o f f our experiments each with six replications.

The differences between the Tagetes species and tomato were very pronounced at all treatment periods (Table I ) . With longer periods of growth, root-knot infection progressively decreases under marigolds but under tomato steadily in- creases. Fallow treatment pots show very slight decrease, suggesting that root-knot viability is little affected and that population reductions are correlated with T'agete.r. In further studies, incorporating Z'. minuta, two crop cycles were included as treatments. At the end of each 35 days, the soil and roots were removed from each pot in turn, the roots were chopped up finely, mixed with the soil and all returned to the pot. The subsequent plant species was then planted. The roots of the tomato indicator plants removed at the end of the experiments were rated for the degree of root-knot galling present (Table II).