Interrelationships of Meloidogyne hapla Chitwood, 1949 with Heterodera schachtii Schmidt, 1871 on Beta vulgaris L. Public Deposited

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  • Self-interactions (effects of reinoculation with the same nematode) in Meloidogyne hapla and Heterodera schachtii on Beta vulpris at different levels of inocula with various population combinations were studied. In M. hapla, the only significant increase of galls was noted in treatments when 250+250 larvae were inoculated at 10-day intervals. Longevity of plants in double inoculated treatments was lower than single inoculated series. Similarly, lower ratios of total soluble/reducing carbohydrates were obtained in double inoculated series as compared to other treatments. Total quantities of B, K, and P were lower in all inoculated plants as compared to non-inoculated series. In H. schachtii, cyst formation was increased from three to five fold in all double inoculation treatments as compared with single inoculated series. Longevity of plants in double inoculated series was lower than single inoculation treatments. Total quantities of B, K, and Mg were lower in all inoculated plants as compared to non-inoculated control series. Lower quantities of Mn, Cu and Zn were observed in most of the double inoculated treatments as compared to single inoculated series. Interactions of M. hapla with H. schachtii at different levels of inocula with all population combinations and different inoculation periods were studied. Results indicated significant reductions of M. hapla galls in all treatments when H. schachtii preceded the latter by ten days in inoculation. This interaction was termed as amensalism with M. hapla serving as an amensal and H. schachtii serving as an inhibitor. Conversely, when M. hapla preceded H. schachtii by ten days in inoculation, there were significant increases in cyst formation by the latter. This relationship was termed as commensalism with H. schachtii serving as a commensal. In both of these interactions, however, the pre-invading parasites acted independently and had a population growth and establishment equal to treatments receiving either of the parasites alone. In treatments when both nematodes were inoculated simultaneously, there were no significant changes in population of either parasite. Relationships of this nature were termed as neutralism. Ratios of total soluble/reducing carbohydrates were lower in treatments when M. hapla preceded H. schachtii. These results also were reflected on plant longevity rate. Although there were variations in longevity of plants in all treatments, the plants inoculated with both nematodes had less longevity than those inoculated With either parasite alone. Further studies with longer periods between inoculations indicated that if the majority of pre-invading parasites (M. hapla) were in the second to fourth stages of development within plants prior to inoculation by H. schachtii, the growth and development of the latter was retarded. Conversely, when majority of pre-invading parasites (M. ahap.la) were at stages of young females prior to H. schachtii inoculation, the growth and survival of the latter was greatly increased. As the pre-invading parasites (M. hapla,) reached stages of fully grown (eggs were not observed) and egg - laying females in plants prior to inoculation by H. schachtii, the growth and development of the latter progressively decreased. Histopathological interrelationships of M. hapla with H. schachtii were studied. Anatomical changes due to M. hapla infection were characterized by regions of hypertrophy and hyperplasia. Hypertrophied cells formed giant cells within stele and their number varied from 4-7 per nematode feeding site. Hyperplastic regions composed of large number of relatively small compacted cells surrounded the giant cells. Syncytia caused by feeding of H. schachtii became dense and multinucleate. They were typically formed within stele and were limited on the side toward the nematode by endodermis or in part by cortical cells. Histological changes in samples exhibiting both nematodes at one feeding site were characterized by presence of the pathological tissues induced by both nematodes. In most cases xylem elements separated the two pathological tissues. In some sections a single wall separated these two pathological tissues and no dissolution of the separating walls was observed in any section. Apparently each nematode developed normally and produced its own characteristic pathological changes of tissue independently from the other nematode. The role of M. hapla as breaker of resistance to H. schachtii in B. patellaris was investigated. A few poorly developed H. schachtii cysts lacking eggs were observed in some treatments when M. hapla preceded H, schachtii by ten days in inoculation, Results indicated that M. hapla may play a role as a predisposing factor to infection by H. schachtii.
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