No abstract

In an effort to select and characterize apple rootstock resistant to apple proliferation (AP), progenies from seven apomictic rootstock selections and their parental apomictic species, Malus sieboldii and M. sargentii, were compared to standard stocks M 9 and M 11. Seedlings derived from open pollinated mother plants were grafted with cv. Golden Delicious and grown under natural infection conditions. The progenies differed greatly in resistance to the AP agent 'Candidatus Phytoplasma mali'. Progenies of M. sieboldii and its descendent rootstock selections D2212, 4608, 4551, and D1131 showed a high level of resistance, whereas progenies of M. sargentii and its descendent selections D1111 and C1828 proved susceptible. M 9 and M 11 showed an intermediate level of resistance. Phytoplasma titer in roots of the M. sieboldii and M. sargentii progeny groups was similarly low, whereas the concentration in the standard stocks was 100 to 5,000 times higher. In trees on most of the resistant stocks, only a minority was colonized in the scion, while in trees on susceptible and standard stocks, infection rate was often higher. Also, the titer in the top of trees on resistant stocks was usually lower than in trees on susceptible and standard stocks. Four progenies derived from open pollinated M. sieboldii and M. sieboldii descendents were subjected to DNA typing using simple sequence repeat (SSR) markers. This study revealed that the selected groups consisted mainly of mother-like plants (apomicts) and type I hybrids (unreduced mother genotype plus one male allele at each locus). Type II hybrids (full recombinants) and autopollinated offspring were rare. In the 4608 progeny, trees grown on type I hybrid rootstocks were significantly less affected than trees on mother-like stocks. In other progenies with fewer or no type I hybrids, trees on type II hybrids and autopollinated offspring suffered considerably more from disease than trees on mother-like stocks.

In the present study, we investigated the natural control of aphids by predators in wheat fields in a low (L) and high-input cropping region (H) of Germany during a 10-year period. Data for the statistical analyses were obtained from weekly after the start of aphid emergence. The mean annual aphid indices, calculated as the sum of Sitobion avenae (Fabr.), Rhopalosiphum padi (L.), Metopolophium dirhodum (Walk.)(Homoptera: Aphididae), were 30.4 and 81.5 · 10 3 aphid days per m 2 , for L and H, respectively. Nine predator fractions were analysed: Coccinella septempunctata L., adults (1) and larvae (2), Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae) adults (3) and larvae (4), syrphid larvae (mostly Episyrphus balteatus [De Geer] (Diptera: Syrphidae)) (5), Chrysoperla carnea Steph. (Neuroptera: Chrysopidae) larvae (6), and adult carabids (7), staphylinids (8) and spiders (9). The two sites were comparable in terms of the mean size of the overall predator community, expressed in predator units (PU): 4.9 PU/m 2 (L) vs. 5.4 PU/m 2 (H). Most predator fractions responded numerically to increasing aphid densities. The numerical response was strongest in syrphid larvae, scarcely detectable in adult coccinellids, and virtually non-existent in epigeic arthropods. Multiple regression models revealed indirect relationships between the weekly overall predator community densities (PU/m 2 ) and individual predator fractions (individuals/m 2 ) and absolute rates of aphid density increase (individuals/m 2 ) one or two weeks after baseline. A site-independent reduction of the aphid density increase to nil (y = 0) was observed at 3.9 to 4.2 PU/m 2 . Consequently, the 2.7 times higher aphid density at H cannot be attributed to the presence of fewer predators or lower effects of the overall predator community or of any individual predator fraction.

Greenhouses in Turkey under integrated pest management can be colonized by a high number predatory flies of the species Coenosia attenuata Stein, 1903 (Muscidae: Coenosia Meigen, 1826. Studies have shown that Coenosia predators do not simply colonize greenhouses from the outside for short periods but instead they are able to complete their developmental cycle in the greenhouse soil and can become established there for a long period of time. C. attenuata is indigenous to the Palaeotropical region. Its prey spectrum includes whiteflies, black fungus gnats and leaf-mining flies. Studies of the natural occurrence of these predaceous flies in greenhouses led to a recognition of the significance of this complex of beneficials for the control of important greenhouse pests. They can build up effective populations under greenhouse conditions, and as non-specific predators can feed on a variety of pest groups and on innocuous species.

In three trials carried out over a period of 24 years, open-pollinated seedlings of Malus sieboldii and M. sargentii and 22 apomictic rootstock selections with either M. sieboldii, M. sargentii or M. hupehensis in their parentage were examined for apple proliferation (AP) resistance in comparison to clonal M. x domestica-based rootstocks M 9, M 11, M 13, stocks of the B (Budagovski) and the Polish P series and M. robusta seedlings. Following experimental inoculation or natural infection the Golden Delicious-grafted trees on most of the M. sieboldii-derived progenies showed a high level of AP resistance expressed by low cumulative disease indices, a high percentage of non or little affected trees, low incidence of the small fruit symptom and non or little effect on vigour. Trees on M 9 and M 11, B 118 and M. robusta seedlings were moderately susceptible while trees on progenies with M. sargentii and M. hupehensis parentage, rootstocks of the P series, B 9, B 490 and M 13 proved highly susceptible. The screening also showed that rootstocks with M. sieboldii and M. sargentii parentage are often highly susceptible to latent apple viruses. Trees on most of the M. sieboldii-based progenies were more vigorous than trees on standard stock M 9, whereas the vigour of some progenies from selections with M. sargentii parentage was in the range of M 9 or even lower. Productivity was often correlated with the vigour.