Suitability of sunflower, Helianthus annuus L., for reproduction of certain plant-parasitic nematodes

Sunflower, Helianthus annuus L., is the second largest oilseed crop in the world, after soybean. The possibility of sunflower being a suitable rotation crop with soybean in fields infested with the soybean cyst nematode, Heterodera glycines Ichinohe, has encouraged interest in growing sunflower in Tennessee. The objectives of this investigation were to (a) study the suitability of selected sunflower cultivars for the reproduction of certain plant-parasitic nematodes, (b) study the effects of increasing initial inoculum densities (Pi) of M. incognita (Kofoid and White) Chitwood on sunflower growth and nematode reproduction dynamics, and (c) study the summer population dynamics of plant-parasitic nematodes occurring in sunflower fields. Ten thousand eggs of either Maloidogyne arenaria (Neal) Chitwood, M. hapla Chitwood, M. incognita, or M. javanica (Treub) Chitwood were inoculated onto plants of 11 sunflower cultivars and tomato 'Rutgers'. Seven hundred fifty Helicotylenchus dihystera (Cobb) Sher or 1,000 Pratylenchus alleni Ferris were inoculated onto plants of 7 sunflower cultivars and soybean 'Pickett-71'. All nematode species were found to reproduce well on all tested sunflower cultivars, although there was some variability among the cultivars. Plants of sunflower cultivars 212 and 800 were inoculated with either 0, 5,000, 10,000, 20,000, 40,000, or 80,000 eggs of M. incognita. Plant height and root weight were found to decrease with increasing inoculum level. Number of females, females/g root, egg production, and eggs/g root of M. incognita all increased with increasing inoculum. Number of eggs/female were unaffected by inoculum level. Cultivar 212 was significantly higher than 800 on plant height, root weight, and egg production, but lower on female/g root and eggs/g root. Thus, these results indicate that cultivar 212 may be more tolerant of nematode feeding than 800. Two sunflower fields were sampled at 3 dates in 1979 and one field which had both sunflower and soybean at 3 dates in 1980. Helicotylenchus pseudorobustus (Steiner) Golden and Pratylenchus scribneri Steiner greatly increased over the sampling period. Very low numbers of Macroposthonia sp., Hoplolaimus galeatus (Cobb) Thome, Meloidogyne sp., Paratylenchus sp., and Xiphinema americanum (Cobb) were also found. The results of this study suggest that nematodes may be a factor in the use of sunflower in rotation with soybean or any other field crops in Tennessee.