Abstract
In Egypt, parasitic weed species, Orobanche crenata Forsk is one of the major constraints to the production of faba bean, which is considered the most important food legume in the country. The broomrape fly, Phytomyza orobanchia Kaltenbach (Diptera, Agromyzidae) is particularly suitable for biological control since it is oligophagous feeding in the larval stage, only on Orobanche species. The objective of the present study is to estimate the number of annual generations of P. orobanchia, using growing degree-days (GDD) in Alexandria region, Egypt. Results revealed that development of Phytomyza immature stages (from egg deposition to adult emergence) required 103.5, 90.0, 79.5, and 93.5 DD through 31, 20, 18, and 16 days for the investigated four generations, respectively. Percentage of infested Orobanche capsules positively increased with increasing accumulated degree-days. A linear model for predicting infested capsules with P. orobanchia through knowing DD was estimated. The constructed model may be used also in predicting Orobanche capsule infestation with P. orobanchia. Results also indicated that estimating the degree-days will help in predicting the occurrence of the first egg laid for P. orobanchia in O. crenata flowers in the field for the first generation and subsequent generations. Knowledge of the Phytomyza activity will provide a prediction for adult emergence and subsequent egg laying and potential damage by larvae according to infestation percent of Orobanche capsules through the successive generations. This may help the biological control programs to justify the required numbers of Phytomyza and adequate time for releases to obtain the maximum destruction of Orobanche seeds.
Highlights
In Egypt, Orobanche crenata Forsk is one of the major constraints in faba bean productions, which is considered the most important food legume in the country
Accumulated degree-days required for development of four generations of P. orobanchia in O. crenata spikes are presented in Table 1 and Fig. 2
Orobanche spikes were examined at the three growth stages: GS 6, 65, GS 6, 69, and GS 7, 79 through all generations of P. orobanchia
Summary
In Egypt, Orobanche crenata Forsk is one of the major constraints in faba bean productions, which is considered the most important food legume in the country. In the West Nile Delta region, the area infested with O. crenata was more than 25,000 feddan (feddan = 4200 m2) (Zaitoun et al 1991). It occurs in about 20% of the total area cropped with faba bean, of which about half suffers low to moderate infestation (less than 5 spikes per m2) and the other half is infested with 5–20 spikes per m2 or more. The strength of broomrape lies in its ability to form a considerable seed bank in soil. A management or eradication program must aim at reducing this seed bank, in order to minimize the production of new seeds and their dispersal to new sites
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