Five in vitro propagated peach scion cultivars (Suncrest, Rio Oso Gem, Compact Redhaven, Redhaven, Jerseyqueen) and two rootstock (Nemaguard and Lovell) were screened in vitro and in microplots for their susceptibility to the root-knot nematode, Meloidogyne incognita. Evaluations in tissue culture for galling were conducted at 5 wk. Trees in microplots were evaluated for 3 years for nematode populations, trunk diameter, and yield. Comparative results indicated that the number and size of galls observed at 5 wk in vitro is indicative of the response of peaches to nematodes under field conditions after three years. Cultivar Compact Redhaven was significantly more tolerant to root-knot than `Lovell' the most widely used peach rootstock. These results suggest that Compact Redhaven might be potentially useful as a rootstock in the Southeast where Nemaguard is used sparingly because of its lack of cold tolerance. In addition, these results indicate that in vitro screening holds promise as a rapid technique for evaluating root-knot nematode resistance.
F.A. Hammerschlag and R.N. Huettel
Aref A. Abdul-Baki, S. A. Haroon, and R. N. Huettel
Susceptibility of tomato (Lycopersicon esculentum Mill) genotpyes to the root-knot nematode Meloydogyne incognita and to heat stress can be evaluated in a single labor- and time-saving operation using a nondestructive in vitro excised root technique. Seeds are sterilized and germinated for 2 days on 1% water agar. Five-mm root sections are grown at 28 and 35 C for 30 days on Gamborg-B medium with and without nematode inoculum. Evaluation criteria include fresh and dry weight and the appearance of juveniles, adults, gulls, and egg masses. Evidence will be presented on the breakdown of resistance to M. incognita under high temperature stress.
Aref A. Abdul-Baki, J.R. Teasdale, R. Korcak, D.J. Chitwood, and R.N. Huettel
A low-input sustainable agricultural system for the production of staked, fresh-market field tomatoes (Lycopersicon esculentum Mill.) is described. The system uses winter annual cover crops to fix N, recycle leftover nutrients, produce biomass, and prevent soil erosion throughout the winter and spring. Yields of tomato plants grown in hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L.) plus hairy vetch mulches were higher than those grown in the conventional black polyethylene (BP) mulch system in 2 of 3 years. Fruit were heavier with the plant mulches than with BP mulch. Eight weeks after transplanting, N levels in tomato leaves were higher with plant than with BP mulch, although the plant mulch plots received only 50% of the N applied to the BP plots. The cover crops had no effect on populations of five phytoparasitic nematode species.
Ghazala P. Hashmi, F.A. Hammerschlag, R.N. Huettel, and L.R. Krusberg
Somaclonal variation has been reported in many plant species, and several phenotypic and genetic changes, including pathogen and pest resistance, have been described. This study was designed to evaluate somaclonal variation in peach [Prunus persica (L.) Batsch] regenerants in response to the root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood. Regenerants SH-156-1, SH-156-7, SH-156-11, and SH-156-12, derived from `Sunhigh' (susceptible) embryo no. 156, and regenerants RH-30-1, RH-30-2, RH-30-4, RH-30-6, RH-30-7, and RH-30-8, derived from `Redhaven' (moderately resistant) embryo no. 30, were screened in vitro for resistance to the root-knot nematode. Under in vitro conditions, fewest nematodes developed on regenerants SH-156-1 and SH-156-11, `Redhaven', and all `Redhaven' embryo no. 30 regenerants. The most nematodes developed on `Sunhigh', `Sunhigh' seedlings (SHS), and regenerant SH-156-7. Nematodes did not develop on `Nemaguard'. In greenhouse tests, fewer nematodes developed and reproduced on the no. 156-series regenerants than on `Sunhigh'. Under in vitro conditions, significant differences among uninfected (control) regenerants, cultivars, and rootstock `Nemaguard' were observed for shoot height and fresh root weights. Significant differences were also observed among infected regenerants, cultivars, and `Nemaguard' for these characteristics, but differences were not observed between control and infected regenerants. Different concentrations of α-naphthaleneacetic acid in half-strength Murashige and Skoog salt medium induced rooting of two peach cultivars, one rootstock, and four regenerants.