Effects of Fertilizer and Pesticides on Soybean Growing in Heterodera glycines-infected Soil.

A nematicide, dibromochloropropane; the fungicides benomyl and maneb; an insecticide, oxydisulfoton; the herbicides trifluralin, linuron, and dinoseb; and fertilizers were applied to Heterodera glycines-infested soil. A resistant soybean cultivar alone produced the highest yield in one test, and its yield was not affected by application of pesticides or fertilizer. In two tests the cultivar that was supposed to be resistant was not. Application of nematicide alone resulted in higher yields of the susceptible cultivar, compared with the untreated check, in only one of three tests. Various combinations of pesticides also resulted in higher yields, and in all cases the nematicide was included. Pesticides and fertilizer must be used with discretion on soybean.

Resistance in Commercial Soybean Cultivars to Six Races of Heterodera glycines and to Meloidogyne incognita.

Soybean cultivars grown in pots in the greenhouse were tested for resistance by inoculation with Meloidogyne incognita or one of six races of Heterodera glycines. Selected cultivars were tested against each nematode isolate. The numbers of cultivars tested against each H. glycines race and the numbers resistant and (or) moderately resistant were as follows: Race 2 - 114 tested, 1 resistant and 9 moderately resistant; race 3 - 170 tested, 56 resistant and 17 moderately resistant; race 4 - 89 tested, 1 resistant and 13 moderately resistant; race 5 - 106 tested, 4 moderately resistant; race 6 - 95 tested, 10 resistant and 25 moderately resistant; race 14 - 81 tested, 2 resistant and 10 moderately resistant. No cultivar was resistant to all races. Meloidogyne incognita was tested on 139 cultivars; 50 were resistant.

Morphometric and serologic comparisons of a number of populations of cyst nematodes.

Thirty-five populations of Heterodera glycines and populations of 15 other Heterodera, Globodera, and Punctodera species were studied morphometrically and some were compared serologically. There was a wide range of each measurement within each nematode population. Except for one soybean cyst nematode population from Indiana, which was a tetraploid and considerably larger than the others, morphometric measurements overlapped. In a discriminant function comparison most of the populations were closely grouped but at least three were rather distinctly separated. Morphometrically H. fici, H. cruciferae, H. schachtii, and H. trifolii were closely associated with H. glycines. Serology indicated a close relationship between H. glycines, H. lespedezae, H. trifolii, H. schachtii, and the Heterodera sp. from Rumex, while H. betulae appeared to be more distantly related.

Infra-species Variation in Reactions to Hosts in Heterodera glycines Population.

Eighteen hosts were inoculated with each of four races of Heterodera glycines. A discriminant function analysis of the reactions of these races to these hosts demonstrated that these races could be separated but not consistently. Then 33 H. glycines populations collected from 13 states and five obtained from Japan were tested on differential hosts. The number of variants discriminated within these 38 populations depended on the number of differentials and the rating system used. When five differentials were used with a (+) or (-) rating system there were six "races," but when 13 differentials were used with a (+) or (-) system there were 25 physiological groups. If an index rating system was used there were 36 groups. Apparently H. glycines is a very variable species and delineation of races varies with criteria chosen.

Development of Heterodera glycines pathotypes as affected by soybean cultivars.

The reproductive abilities of four races of Heterodera glycines were compared on soybean cultivars by using single cyst or mass inoculations. Progeny transfers were used to determine changes in reproduction of H. glycines. Reproduction of all races (1, 2, 3, 4) was best on 'Lee' and poorest on P1 88788. The size of females produced and numbers of eggs/female of the different races varied with the cultivar. Races 1 and 3 appeared to contain low populations of Races 2 or 4. Races 2 and 4 were best selected by a series of transfers on 'Pickett' soybean.

The Effect of Temperature and Moisture on the Survival of Heterodera glycines in the Absence of a Host.

Soybean-cyst nematode larvae survived in water up to 630 days, depending on incubation temperature. Most larvae were killed when ice crystals formed in water, and all died after 1 day at 40 C. At temperatures of 0, 4, 8 and 12 C, larvae survived for the duration of the experiments (630 days). From 16 to 36 C, survival was inversely correlated with temperature. In naturally infested soil, nematode survival was similax but more extended and related to moisture level. Larvae survived 7-19 months in flooded soil, 29-38 months in dry soil, and for 90 months in soil maintained near its field capacity.

Life Cycle, Host Range, and Reproduction of Heterodera betulae.

Heterodera betulae, a cyst-forming nematode, originally recovered from roots of river birch in Arkansas, appears to have a limited host range. Of 80 plant species in 20 families tested, only five species of Betula and Cleome spinosa supported reproduction. The minimum time for a complete life cycle was 52 days at 28 C. No reproduction occurred at 31 C or above, and development was very slow below 20 C. Successful population propagations from single larvae demonstrated that males were not necessary for reproduction.