The use of some agricultural practices such as tillage and irrigation affected the natural population of Phytomyza orobanchia Kalt., the main active bioagent against broomrape in Egypt. During March of 2010/2011 season, fleshy plants of Orobanche crenata shoots were collected from faba bean fields. Under semi-field conditions, whole plants of Orobanche crenata shoots were buried at different depths (5, 10, 15, 20 and 25 cm) in sandy, sandy-loam and clay soil in pots and treated with three treatments of water (moistened, flooded and dry). At the beginning of the new activity season 2011/2012, emergence percentages of the broomrape fly, P. orobanchia from Orobanche shoots contained diapaused pupae were estimated, which were buried under the effects of different agricultural practices. Results revealed that the emergence percentage of Phytomyza adults had significantly reduced with increasing the depth of buried O. crenata shoots. Highest mean emergence percentage was (52.31%) occurred from puparia in Orobanche shoots buried in moist soil. On the other hand, sandy-loam soil was enough for emergence of 42.40%. It could be recommended to bury Orobanche shoots containing diapaused Phytomyza pupae at 5 cm depth after collected during March. After that it is recommended to cover the shoots with moistened and sandy-loam soil in order to increase the rate of initial Phytomyza population working in faba bean field against Orobanche crenata at the start of new seasons activity.
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The broomrape fly, Phytomyza orobanchia Kalt. has three generations annually (Shalaby, 1974; Al-Eryan, 1996). At the end of Orobanche season, larvae of last generation migrate from Orobanche capsules towards the aerial and underground parts for pupation to stay in diapause till the subsequent season (Tawfik et al., 1976; Al-Eryan and Zaitoun, 1998). The greatest numbers of diapaused pupae occur in the underground parts of the plant (Mihajlovic, 1986). The third generation faces some of environmental resistance factors such as agricultural practices and natural enemies (insect parasitoids) causing significant reduction in Phytomyza population size (Kroschel and Klein, 1999). In this respect, the fleshy Orobanche shoots collected in early March were completely free from the parasitoid (Tetrastichus phytomyzae), on one hand and since P. orobanchia pupate and enter diapause in the underground parts of Orobanche, it faces different death factors such as, some agricultural practices until the new activity season, on the other hand. Factors limiting the natural population of P. orobanchia such as pupal parasitoids, destruction of pupae by tillage and flooding can be avoided by means of controlled rearing (Abu-Shall, 2001).
The present study was carried out during 2010/2011 faba bean season to estimate the population status of P. orobanchia with some agricultural practice (tillage and irrigation), aiming to reach high rates of the initial P. orobanchia population during the new activity season 2011/2012 against O. crenata spikes to guarantee a quick build-up of their population.
MATERIALS AND METHODS
Sampling and estimation natural infestation rates by diapaused Phytomyza pupae: During March of 2010/2011 season, fleshy plants of Orobanche crenata shoots (Hess et al., 1997) infested with P. orobanchia were collected from faba bean fields in the Agricultural Research Station (ARS), Faculty of Agriculture, Alexandria University, Egypt.
In the laboratory, a random sample of 20 Orobanche shoots were picked up and dissected when the pupation took place. The Orobanche shoots were examined, to detach and count the diapaused pupae of Phytomyza per stem. After that, the mean number of diapaused pupae per stem was determined as follows:
Effect of some agricultural practices on P. orobanchia under semi-field conditions: At the end of 2010/2011 season, whole plants of O. crenata shoots infested with diapaused pupae of Phytomyza were buried at different depths 5, 10, 15, 20 and 25 cm in sandy, sandy-loam and clay soil in plastic pots (60 cm length and 20 cm width) to be similar to tillage under filed conditions. Each type of soil was treated with three treatments of water (moistened, flooded and dry) to be similar to irrigation under field conditions. Each treatment consisted of 3 replicates and each replicate of 5 Orobanche shoots.
Natural activity of initial Phytomyza population during the new season: At the beginning of the subsequent season 2011/2012, the glass tube was hung up at 10 to 15 cm height above the soil surface on wooden stake in each pot. Piece of cotton saturated with honey solution was put in the glass tube (replaced weekly) for feeding the emerged Phytomyza adults, (Abu-Shall, 2001). A plastic funnel was upset on the glass tube opening (Fig. 1). The glass tube was connected to the narrow opening of the plastic funnel, through which, only the Phytomyza adults could pass into the funnel to glass tube. Pot contents were covered with metal-screen cloth cage (Fig. 2). For bringing the glass tube out, a small window of 8x10 cm was cut into the cloth cage to collect and count the emerged adults of Phytomyza weekly.
To calculate the percentage of emerged Phytomyza adults at the end of season as follows:
Statistical analysis: Data were subjected to the analysis of variance test (ANOVA), with mean separation at 5% levels of significance, Computer program IRRISTAT and Duncans Multiple Rang Test was used to compare the averages according to the method of Snedecor and Cochran (1967).
|Fig. 1(a-e):||Glass tube was hung up on wooden stake and provided with piece of cotton saturated with honey solution, which connected to the narrow opening of the plastic funnel, (a) Wooden stake, (b) Glass tube, (c) Piece of cotton saturated with honey solution, (d) Plastic funnel and (e) Plastic pot contain on whole plants of O. crenata shoots infested with diapaused Phytomyza pupae, which buried in different depths and soils with three treatments of water|
|Fig. 2(a-c):||Metal-screen cloth cage with a small window was covered pot contents, (a) Metal-screen, (b) Metal-screen with cloth cage cover the previous plastic pot contents in Fig. 1 and (c) Metal-screen cloth cage provided with a small window (8x10 cm)|
The natural capacity of P. orobanchia to reduce the Orobanche population is limited by several factors such as low temperature, cultural practices (soil preparation, crop rotations, irrigation and the use of insecticides against crop pests) and natural enemies (microorganisms and parasitoids) (Kroschel and Klein, 1999). Also, the use of intensive agrotechnical measures includes the following factors affecting the mass reproduction of Phytomyza populations: soil cultivation, crop rotation and pesticide application.
|Table 1:||Emergence percentages of Phytomyza adults from Orobanche shoots buried at different depths and soil with three water treatments|
|Values are means of 3 replicates each of 5 Orobanche shoots per treatment. Means followed by the different letter are significantly different at the 5% level by DMRT, L.S.D0.05 (Type of soil) = 0.85, L.S.D0.05 (Buried depth of Orobanche shoots) = 1.26, L.S.D0.05 (Treatments of water) = 0.68|
In autumn and spring, during the preparation of soil for sowing, the broomrapes were ploughed in together with the pupae of Phytomyza overwintering generation. In spring, the flies did not manage to go out through the deeper layers of soil, so they die in high percentages, thus decreasing the initial Phytomyza population during the sprouting and the beginning of flowering of broomrapes (Mihajlovic, 1986).
Emergence percentages of Phytomyza adults in the new season from diapaused pupae in Orobanche shoots buried in different depths and soil with three treatments of water are presented in Table 1. Results revealed that emergence percentages were 58.89, 52.01, 39.19, 21.82 and 15.60% from different depths 5, 10, 15, 20 and 25 cm, respectively. At the level of treatments of water, these were 52.31, 33.40 and 26.79% from moistened, dry and flooded soil, respectively. Irrespective of treatments of water and bury depths of Orobanche shoots, it was 36.72, 42.40 and 33.39% emergence in sandy, sandy-loam and clay soil, respectively.
Statistical analysis revealed that emergence percentages of Phytomyza adults, significantly, decreased with increasing the depth at which Orobanche shoots containing diapaused pupae were buried. This finding indicated that 5 cm depth to bury Orobanche shoots, significantly, led to emergence of highest percentage of Phytomyza adults in the new season compared with other depths. On the other hand, moist and sandy-loam soils were significantly rich with emergence percent of Phytomyza adults in the new season.
In this regard, Abu-Shall (2001) indicated that the dry (both clay and sandy) soil is the optimum type of soil for preservation and storage the collected pupae of P. orobanchia till the next season. Also, the suitable depth to bury P. orobanchia pupae (5-10 cm) should be undertaken in release programs to improve emergence of Phytomyza adults. While, Trenchev (1981) found that the pupae of P. orobanchia which have been buried at a depth of 20-25 cm resulted to an emergence rate of only 21% and the beneficial role of the fly was diminished by autumn ploughing. Moreover, the deep tillage and the incorporation of Orobanche shoots by ploughing may have caused a mechanical destruction of pupae and adults were only able to emerge after hatching from a soil depth of maximum 20 cm. For the same target, Cubero (1983) pointed out that pupae could be destroyed by irrigation.
At the level of the effect on O. crenata, Zahran (1982) noted that subsoil ploughing did not differ significantly from conventional tillage in its effect on O. crenata in faba bean. Consequently, deep plowing will be a solution only in limited cases. Zero or minimum tillage so far provided hardly significant differences when compared to conventional tillage (Kukula and Masri, 1984). This finding is conflicting with the effect of tillage on emergence Phytomyza adults from diapaused pupae. While, several observations document the less severe Orobanche infestation under high moisture levels or after periods of flooding (Cubero, 1983). Zahran (1982) reported a decrease of O. crenata infestation in faba bean after two weeks of flooding prior to the sowing of the crop in Egypt. Also, he reported about 65% reduction in O. crenata infestation in faba beans following a flooded rice crop when compared with fallow. On the other hand, the respective values of reduction in Orobanche spikes were found to be 0 and 25% with 10 and 30 day irrigation interval without pre-sowing flood, compared with 4 and 36% with pre-sowing flood (Hassanein and Salim, 1999). Also, it was found that irrigation during summer reduced the infestation with O. crenata in Spain (Mesa-Garcia et al., 1984). This finding is conflicting with the effect of flood on emergence Phytomyza adults from diapaused pupae. According to Van Hezewijk et al. (1993), it was found that a prolonged period of moistening induced secondary dormancy in O. crenata seeds. There are some reports that indicated a reduction of Orobanche infestation after a period of flooding, as for rice, but the mechanism is not yet fully understood. The decline of the Orobanche population may be a result of an enhanced microbial activity and decay of the seeds or shoots. Anaerobic conditions in the soil, which favor the formation of toxins that lead to a decrease in the viability of the seed population, may also contribute to the detrimental effect on broomrape infestation (Sauerborn and Saxena, 1986; Mohamed-Ahmed and Drennan, 1994).
Another approach to increase the initial population of Phytomyza was reported by Bronstejn and Kabulov (1961) who stated that the simplest method to enhance the survival rate of pupae in the field is to store collected Orobanche shoots at field borders. A mechanical destruction caused by tillage there can be avoided. In the former USSR, (Tsybulskaya and Skoklyuk, 1978) calculated the number of infested Orobanche stems required for release of the fly over one hectare. Therefore, the best method is the stems containing puparia should be released in the field as soon as flowers appear on the weed and bury them in special trenches cut between the crop rows, which are then filled up with a 20 cm layer of soil to pass and to purify the population.
From semi-field experiment, fleshy Orobanche shoots collected during March and buried on depth 5 cm in moist and sandy-loam soil caused the highest emergence percent of Phytomyza orobanchia, being required to increase the rate of initial Phytomyza population in faba bean fields against Orobanche crenata in the new activity season. These findings may be helpful in the future field studies which related to the damage effects of some agricultural practices such as tillage and irrigation. This study should be undertaken in release programs for increasing the population of P. orobanchia first generation which play an important role in biological control of the emerging O. crenata. Consequently, the number of infested Orobanche shoots contained diapaused Phytomyza pupae, which are required for early release of the fly adults in field should be calculated per feddan. After that, Orobanche shoots could be buried at 5 cm depth at field borders and covered with moistened and sandy-loam soil.
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