General Commission for Scientific Agricultural Research-
Lattakia Research Center
Tishreen University, Faculty of Agriculture
Branched broomrape Orobanche ramosa L. (Orobanchace) is considered as a serious holoparasitic weed on many crop plants, especially solanaceous plants (Solanaceae). The aim of this study is to (1) determine the distribution of host plants and phytophagous insects (especially Phytomyza orobanchia Kalt.) for branched broomrape along the Syrian coastal region, (2) test the efficiency of herbicide for controlling O. ramose, and (3) evaluate the sensitivity of some tomato cultivars against O. ramosa.
Many solanaceous fields, plastic houses and surrounding fields, and ornamental nurseries were surveyed for O. ramosa during 2002/2003-2005/2006 growing seasons. Branched broomrape samples were randomly collected from infested fields. Samples of 5625 shoots and 35878 capsules were inspected by dissection.
The results have shown that O. ramosa distributed in various sites of surveyed region up to more than 1300m above sea level. Infestation rate was 70.33% of studied fields with different infestation severity. O. ramosa was found parasitizing many species of vegetable crops and wild weeds, and it has been recorded on /25/ plant species, 8 species of them are recorded for the first time and those hosts are: Hibiscus esculentus L., Orchorus olitorius, Ociumum basilicum L., Peperomia caperata, , Zinnia elegens, Pelargonium roseum, Calendula arvensis L, Vernica persica Poir.
The results indicated that the agromyzid fly Phytomyza orobanchia infests O. ramosa and the larvae feed on seed capsules and shoots, naturally distributed in O. ramosa infested solanaceous fields and plastic houses, with 94.8% distribution rate of studied fields. P. orobanchia was found during year months except February, and considered to be the only specific insect on O. ramosa, where its larva feeds in high efficiency on seeds and shoots.
P. orobanchia infestation rates were different from one region to another, and from on field to another in the same region, and from season to another during the time of this study. These rates reached 100% in some fields. The highest density of larvae and pupae were in capsules. The feeding activity on capsules and shoots was started in the middle of March in the same time of shoots emergence of parasitic weeds, and was increased to reach its peak in May and June. Larvae feeding has caused significant reduction in the weights of infested shoots and capsules in comparison with healthy one, and the larvae in the third instar was more efficient than larvae in the first and second instars. The number of seeds in infested capsules with larvae in the 3rd instar was reduced by 86.18%. The results of comparison study between P. orobanchia measured parameters on O. ramosa infecting tomato and eggplants plants showed that, the rates of infestation of this insect and the total number of larvae and pupae were higher on O. ramosa on tomato. A parasite on P. orobanchia was found in ratio 4.74% as the mean of three seasons.
Three doses of the herbicide Imazapic (2,5, 5 and 7.5 g/h) were tested for their efficacy in controlling O. ramosa on mulched and non mulched tomato plants grown in plastic houses. Herbicide application was achieved with irrigation water, and before shoots emergence. Results showed that, the three doses of Imazapic were efficient in controlling O. ramosa and they caused significant reduction in number of emerged shoots/m², dry and wet weight of these shoots. The efficacy rates measured on number of shoots/m² for three used doses in non-mulched cultivation were 46, 90.28 and 94.64%, respectively. Toxicity symptoms were found on some tomato plants treated with 7.5 g.h, causing negative influence on tomato crop production, where 2.5 g.h caused increasing production.
The sensitivity of some tomato cultivars (Astona, Douplo, Cartica, Huda, Amal) planted in Syria to O. ramosa has been studied, and found to be sensitive to O. ramosa, with various response among cultivars. The development of O. ramosa infestation was different due to cultivars, where it was quick in Astona, Douplo, and Huda cultivars in comparison with infestation of Amal and Cartica, which developed rather slowly. The severity and rates of infestation were different between studied cultivars; Amal was significantly less sensitive than other cultivars due to the number of flowering clusters and plant height.
In conclusion, this study showed wide distribution of O. ramosa and its wide host range, some of them of high economic importance. P. orobanchia as a parasite on O. ramosa may have promising role in controlling this weed as a component of its integrated management.