الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
Abstract
The root-knot nematodes, Meloidogyne incognita (Mi), and wilt-fungus, Fusarium oxysporum f. sp. lycopersici (Fol), devour considerable amount of many agricultural crops including tomato plants Lycopersicon esculentum. Management of these pathogens by cultivating resistant or tolerant plants has an advantage over other measures. It relieves farmers from costly chemical protection and for higher yield and acceptable agronomical extra efforts.
Experiments of this investigation aimed mainly to find out tomato cultivars, as major vegetable crop, that possess adequate resistance or tolerance to Meloidogyne incognita (Mi) and/or Fusarium-wilt fungus, Fusarium oxysporum f. sp. lycopersici, infections to avoid crop loss in fields and to disinfect tomato seedlings in nurseries. In this respect, five tomato cultivars namely, Hyb.ypeel 303, H 9035, ALISSA F1, Jakal and Malika, which cultivated by Egyptian growers on a large scale, were chosen for screening varietal test against both pathogens. The obtained results could be reviewed into three groups according to rate of nematode reproduction (Rr) and rate of wilt severity (Rws) parallel with plant growth reaction. First, a resistant plant group comprising Hyb.ypeel 303 and H 9035 cultivars. This was followed by a second tolerant plant group comprising ALISSA F1 cultivar. Lastly, the third susceptible plant group containing the other tomato cultivars (Jakal and Malika cultivars). As with those susceptible tomato cultivars, they were excluded from advanced study because they have no promise for limiting the target pathogens.
The selected tomato cultivars (Hyb.ypeel 303, H 9035, ALISSA F1) were evaluated in pot-experiment for rating their levelʼs response against increasing inoculum levels per pathogen. The results revealed that, tomato Hyb.ypeel 303 cultivar possessed a complete resistance to all inoculum levels of both pathogens. In addition, tomato cultivar H 9035 possessed an incomplete (partial) resistance to low and moderate levels of infections by both pathogens. On the other hand, tomato ALISSA F1 cultivar was found to be tolerative against low and moderate inoculum levels of both target pathogens.
To monitor the potential interaction between both pathogens into the tested tomato cultivars, an experiment was carried out using concomitant infections simultaneously. The results demonstrated that, both Mi and Fol were interacted mutually in H 9035 and ALISSA F1 cultivars. Also, it was observed a marginal stimulative effect occurred via wilt symptoms accompanied with decreasing root galling and final nematode population. Meanwhile variable inhibition degree of plant growth was noticed. As with Hyb.ypeel 303 cultivar, no interaction occurred between both pathogens since no infection signs were observed.
To clarify the effect of one pathogen on the other in tested tomato cultivars, an explanatory experiment was carried out using increasing inoculum levels of one pathogen jointed with a fixed inoculum level of the other partner. As with the partial resistant cultivar (H 9035), the results indicated that, Fol did not affect nematode reproduction. While, nematodes could increase fungal wilt severity profoundly. As with tomato ALISSA F1 cultivar, data showed that, nematode reproduction was affected inversely by Fol but, nematode infection could increase fungal wilt severity. As regard to tomato Hyb.ypeel 303 cultivar, the infection by both pathogens was undetectable. These data revealed that, Mi nematode could increase plant susceptibility towards Fusarium wilt fungus whereas fungal infections could decrease nematode population in ALISSA F1 cultivar while nematode population was not disturbed in H 9035 cultivar. Also, the mutual effects between both pathogens are density-dependent.
To demonstrate the role of one pathogen in modifying the host cultivar to the other partner, an experiment was achieved by predisposing the roots of a host cultivar to one pathogen while the other pathogen was delayed consequently. The results revealed that, Mi nematode pre-infection could stimulate wilt severity vigorously in both H 9035 and ALISSA F1 cultivars. On the other hand, Fol could stimulate Mi population in H 9035 cultivar and suppress Mi population in ALISSA F1 cultivar. As regard to Hyb.ypeel 303 cultivar, a total resistance to both target pathogens was recognized. In addition, the interaction between involved pathogens seems to be time-dependent.
To detect the possible role of translocatable substances induced by involved pathogen, split-root experiment was carried out by adding Mi in a half root and after 7 days Fol was employed in the opposite half root system and vice-versa was achieved in another treatment. The results realized that, early nematized half root of H 9035 and ALISSA F1 cultivars could induce severe wilt symptoms in entire plant. On the other hand, early fungal diseased half root did not aggravate Mi reproduction. As with Hyb.ypeel 303 cultivar, the results showed no infections by both pathogens occurred in both halve roots. Generally, these results demonstrated that, stimulative effects of wilt symptoms by Mi infection may be attributed to physiological changes in the host via translocatable substances from half part of the root to the whole plant.
For understanding the nature of mutual relations between Mi and Fol, infected and disinfected half roots in split root experiment, were tested phenolically. The obtained results in all infected plants with Mi or Fol indicated that, increased phenols were proportional to low and nul counts of nematode populations or rate of fungal wilt severity as shown in H 9035 and Hyb.ypeel 303 cultivars. Conversely, the low phenolic constituents that detected in ALISSA F1 cultivar was associated with high counts of nematode populations as well as rate of severe wilt disease. In double infections, Mi infection in one half root could induce fungal wilt symptoms as shown in H 9035 and ALISSA F1 cultivars.
In conclusion, the root-knot nematode and Fusarium wilt fungus interacted positively on tomato plant ALISSA F1 (tolerant cultivar) and tomato H 9035 (partial resistant cultivar) to both pathogens. This interaction between both pathogens could be attributed to density-dependent, time-dependent, physiological changes in the host, translocatable substances induced by each pathogen and lastly, to the mechanical damage to roots caused by nematode penetration and development. However, these collective data pointed that, the nature of interaction between Mi and Fusarium wilt fungus is physiological rather than physical.
from nematological point of view, to gain maximal benefit from wilt-resistant or tolerant cultivars, it is recommended to control root-knot nematodes which are responsible for predisposing these cultivars to attack by the Fusarium wilt fungus. As regard to completely resistant cultivar (Hyb.ypeel 303), it is recommended to cultivate it in a suitable long crop rotation to avoid raise up of pathotype offspring of nematodes. As well known, activity and infectivity of root-knot nematodes are of lowest level in winter season. Therefore, cultivating such tomato cultivars in cold weather can protect them from nematode infection and, in turn, from Fusarium wilt fungus.