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Model Short Communication

Suppression effect of Capsicum chinense Jacq. on Southern rootknot nematode [Meloidogyne incognita (Kofoid and White)] in peppers and tomato

J. K. PETERSON and H. F. HARRISON
USDA-ARS Vegetable Laboratory, 2875 Savannah Highway, Charleston, SC 29414, USA
Phone (Office): +390881741632, FAX (Office): +390881741632, Phone (Home): +390881686273, E. Mail: .....................

(Received in revised form: ------------)

ABSTRACT

We evaluated the available sources of C. chinense for resistance to M. incognita and found that all commercial sources of the two types (Habanero and Scotch Bonnet) were moderately susceptible or susceptible. However, four heirloom cultigens, all of the Scotch Bonnet type, showed levels of resistance similar to resistant C. annuum. Three of the cultigens were studied released as PA-353, PA-398 and PA-426

Key words: Capsicum annuum, Capsicum chinense, companion planting, Lycopersicon esculentum, Meloidogyne incognita, pepper, rootknot nematode, tomato

'Correspondence author

INTRODUCTION

In a greenhouse study it was observed that roots of the nematode (Meloidogyne incognita) susceptible tomato (Lycopersicon esculentum Mill.) cv. 'Rutgers' showed reduced galling when intertwined with roots of a nematode resistant pepper (Capsicum chinense Jacq.) 'Scotch Bonnet', growing adjacently in the bench. Thies et al. (6) reported that a highly nematode resistant Cayenne pepper (Capsicum annuum L.) used as a rotational crop inrootknot infested fields allowed subsequent successful growth of a highly susceptible pepper. These observations indicate that companion planting with nematode resistant peppers may provide adequate protection to susceptible vegetable plants. This study was designed to confirm these observations and provide a quantitative measure of the efficacy of the proposed companion planting.

MATERIALS AND METHODS

The Capsicum annuum breeding line PA-136 (I) and the tomato cultivar 'Rutgers' were used as susceptible plants. The highly nematode resistant G. chinense breeding line PA-426 (2, 3) served as companion plant. A one week old tomato or susceptible pepper seedling was planted in the center of a 12 L pot, containing a mixture of 50% pure coarse sand and 50% of a commercial peat, vermiculite mixture. The susceptible, center plants were inoculated with 10 ml of a nematode egg suspension (3000 eggs) in water, dripped around the stem of the susceptible plant. The egg suspension was prepared from infected peppers as described by Hussey and Barker (5). After inoculation the pots were thoroughly watered. An experiment, with either a susceptible pepper or tomato, consisted of two treatments viz., number of companion plants per pot (0,1,2,4) and inoculation with nematode (not inoculated, inoculated). The treatments were replicated 6 times and the pots were arranged in a completely randomized design and the experiments were repeated over time. One full set of experiments was conducted in winter, when greenhouse temperatures ranged between 20-29 C and one set in summer when temperatures -ranged between 24-32 C. Gall indices were independently estimated by two persons and the numbers were averaged for each plant. The following scale was used: I -no galls; 2 -few galls, root system fully intact; 3 -many galls, root system in good condition; 4 -large number of galls, throughout root system, root system discoloured, barely functioning; 5 -massive number of galls, degradation of root system. Data from two complete experiments were combined for analysis of variance and means were separated using Duncan's Multiple Range test at P = 0.05.

RESULTS AND DISCUSSION

The nematode resistant pepper companion plants had no visible infection and significantly reduced galling in the susceptible tomato or pepper plants (Table 1). The susceptible tomatoes and peppers showed the same trend; reduced galling with increasing numbers of companion plants. Dry weights of the root systems of the susceptible tomato or pepper plants increased with more galling, even though the number of thin feeder roots decreased sharply when no companion plants were present. When four companion plants were present, root dry weights of the susceptible plants showed no significant differences between infected and non-infected plants (Table 2 and 3). Root dry weights of susceptible versus resistant plants are presented separately, because the infected tomato plants attained more dry weight in winter (Table 2, Experiment 1) than in summer (Table 2, Experiment 2). Root dry weights of the infected nematode susceptible pepper plants did not show significant differences between infected and non-infected plants (Table 2 and 3). Root dry weights of susceptible versus resistant plants are presented separately, because the infected tomato plants attained more dry weight in winter (Table 2, Experiment 1) than in summer (Table 2, Experiment 2). Root dry weights of the infected nematode susceptible pepper plants did not show significant differences between the two seasons (Table 3). When four companion plants were present, their total root dry weight was approximately 1.3 g/L. At this root density the average gall index for the susceptible tomato plants declined from 4.8 (degrading root system) to 3.3 where the root system was in good condition. Similarly, the average gall index for the susceptible pepper went from 3.6 (large number of egg-masses, root system poorly functioning) to 2.2 (root system intact).

CONCLUSIONS

Fery and Thies (2) evaluated the available sources of C. chinense for resistance to M. incognita and found that all commercial sources of the two types (Habanero and Scotch Bonnet) were moderately susceptible or susceptible. However, four heirloom cultigens, all of the Scotch Bonnet type, showed levels of resistance similar to resistant C. annuum. Three of the cultigens were studied in detail (3) and released as PA-353, PA-398 and PA-426 (4). The resistance in C. chinense was conditioned by a single dominant gene, which is allelic to the dominant gene that conditions much of the resistance in C. annuum. It might be expected that sources of C. annuum or C. chinense which have this dominant gene could afford protection against M. incognita when used as companions with susceptible vegetable plants.

ACKNOWLEDGEMENTS

The authors are thankful to Andrea Gilliard for her valuable contribution to this paper.

REFERENCES

(Recent References of last 10-years [Arranged in Alphabetical Order] are preferred)
  • Dukes, P.D., Fery, R.L. and Thies, J.A. (1997). PA-136 Cayenne pepper, an exceptional host for production of southern root-knot inoculum. HortScience 32: 335.
  • Fery, R.L. and Thies, J.A. (1997). Evaluation of Capsicum chinense Jacq. cultigens for resistance to the southern rootknot nematode.HortScience32: 923-926.
  • Fery, R.L. and Thies, J.A. (1998). Genetic analysis of resistance to the southern root-knot nematode in Capsicum chinense Jacq.Journal of American Society of Horticultural Sciences123: 1008-1011.
  • Fery, R.L. and Thies, J.A. (1998). PA-353, PA-398 and PA-426: southern root-knot nematode-resistant Capsicum chinense Jacq. germplasm lines.HortScience 33: 760- 761.
  • Hussey, R.S. and Barker, K.R. (1973). A comparison of methods of collecting inocula of Meloidogyne spp., including a new technique. Plant Diseases Reporter 57: 1025-1028.