Effects of Arbuscular Mycorrhizal Symbiosis (Glomus intraradice) on Egyptian Broomrape (Orobanche aegyptiaca. Pers) in Cultivated Tomato (Lycopersicon esculentum Mill.)

Mycorrhizal symbiosis is one of the most popular and highest symbiotic relationship in plant kingdom. Most plants (about 80% of vascular plant species) have at least one type of mycorrhiza. Arbuscular mycorrhizal fungies are the most important endomycorhiza fungi that play an important role in agriculture.
In order to evaluate the effect of arbuscular mycorrhizal (Glomus intraradice) symbiosis to control Egyptian Broomrape (Orobanche aegyptiaca. Pers) in cultivated tomato (Lycopersicon esculentum Mill.) growth, a glasshouse experiment was conducted in CRD design with four replications in Shahrekord university in summer 2014. Treatments consisted of four arbuscular mycorrhizal levels (50, 100, 150 and 200 kg ha-1) and two control treatments of weed free and weed infested treatments, respectively. In this experiment, seeds of speedy tomato cultivar planted in the bed that consisted of coco peat and peat moss were transplanted to the pots. Pots with diameter 20 and height 15 cm were filled with soil in the ratio 4: 1: 1 manure, sand and clay respectively and with 50 mg of Orobanche seeds that were collected in the previous year. It should be noted that the soil combination was disinfected at a temperature of 80OC for 72 h to reduce the potential effects of soil microbial population in reducing Orobanche germination. The fungal inoculation, containing sandy soil fungal body parts and organs fungal root was then added to each pot. Fungi strain was provided from the plant protection clinic located in Hamadan. Also, nutrition of tomato after being transplanted to pots was carried out with foliar application of complete micronutrient of 20-20-20 every 7 days under glasshouse condition. At the end of the season, were measured number of stems, number of nodules on the roots of tomato, time of emergence of orobanche flower on the soil surface, orobanche dry weight and tomato root and shoot dry weight. Statistical analysis of the data in the end of experiment collected on the characteristics of tomato and broomrape (after normality test of Kolmogorov - Smirnov) was done separately using software SAS V 9.2 and the comparisons were done with Fisher LSD test at the 5% and 1% levels and drawing graphs in Excel.
The results showed that among arbuscular mycorrhizal fungi treatments, two levels of 50 and 100 kg ha-1 in most cases, orobanche and tomato traits had no significant effect within the orobanche infested control treatment. With the possible existence of uniform density of orobanche seeds ready to germinate in the surroundings of tomato root and absence of adequate colonization by the fungies, these treatments will not be able to prevent the germination establishment of weed on tomato roots. Lack of adequate root colonization can firstly be due to the lack of sufficient numbers of fungi and secondly because of the unsuitable growth environment conditions for fungal propagation. But the treatments of 150 and 200 kg ha-1 decreased the number of nodules on the roots of tomato, orobanche dry weight, and time of emergence of orobanche flower on the soil surface, ratio of orobanche dry weight to tomato shoot dry weight. The difference may be due to the high fungal mycorrhiza colonization on the tomato roots that has led to a significant level of tomato root covered with the fungus, thereby was prohibited the haustorium penetration of orobanche into the root host. The host plant roots do this effect with the release of molecular signals called branching factors (BFs) that induced a wide branching of fungal hyphae. Whereas the treatments of 150 and 200 kg ha-1 increased tomato shoot dry weight and the percentage of tomato root dry weight to shoot dry weight. Even in these two measured traits, the treatments of 150 and 200 kg ha-1 were also transcended on weed-free treatment. Generally, because of no of significant differences between the two treatments of 150 and 200 kg ha-1, utilization of 150 kg ha-1 arbuscular mycorrhizal fungi due to reduction of the orobanche growth and promotion of tomato growth was the best treatment among them. Positive performances of mycorrhiza fungi in reducing broomrape pollution and increasing tomato growth have different reasons. Three main reasons of this research and the previous research laboratory have been established as follows:1) The existence of this fungus causes tomato root covering by the fungal hyphae to be occupied by orobanche haustorium.
2) Tomato roots colonized by the fungus have less germination stimulant compounds.
3) The proper functioning of fungal hyphae increased the uptake of nutrients, particularly phosphorus that produce more favorable growing conditions for tomato even compared to the control without orobanche.
Generally, it seems that regarding the results of treatments of 150 and 200 kg ha-1 in arbescular mycorrhiza fungi in this study, these results can be further studied under field conditions to be more confidently recommendable. Because of the highly dominance of variable in field conditions such as management, climate and the environmental effects can intensify or weaken the effects of treatments.