Effects of sowing date and vernalisation on the growth of winter barley and its resistance to powdery mildew (Erysiphe graminis f.sp. hordei)

Detailed studies on the production of individual leaves, and the development of powdery mildew on them, were made in field plots of winter barley sown on different dates. The greater severity of the disease on early-sown than on later-sown seedlings during the autumn and winter can probably be explained mainly by changes in the abundance of inoculum and the suitability of the weather for infection. Results from glasshouse experiments suggest that the differences may be reinforced by direct effects of vernalisation on the susceptibility of seedlings to the disease. Contrary effects of sowing date on mildew severity during summer are probably due to the progressively greater resistance to mildew of the later-formed than of seedling leaves, and the earlier appearance of corresponding leaves on early-sown than on later-sown plants. Early sowing can also increase the total number of leaves produced per stem. Therefore, because resistance of the leaves increases progressively, the maximum degree of resistance expressed by the later-formed (e.g. flag) leaves will often be greater on early-sown than on later-sown plants.     

A seed treatment for the control of Pythium damping-off diseases and Peronospora parasitica on brassicas

In soil inoculated with Pythium ultimum or Pythium irregulare, seed treatment with either Apron 70 (=1 g metalaxyl and 1 g captan/kg seed) or thiram gave control of pre-emergence damping-off of Brussels sprout and cabbage seedlings. On cauliflower, Apron 70 was significantly more effective than thiram. No post-emergence damping-off occurred in either of these crops or in oil-seed rape following seed treatment with Apron 70 whilst post-emergence losses from untreated seed ranged from 10·2–19·4% and from thiram treated seed from 5·7-7·4%. Apron 70 gave complete control of Peronospora parasitica on cauliflower inoculated 10 days after sowing; thiram was ineffective. Following seed treatment with Apron 70, metalaxyl was detected in the cotyledons, true leaves and roots of cabbage seedlings up to 4 wk from sowing.     

Populations of the phorid fly Megaselia halterata on an experimental mushroom unit over four years

Populations of phorid flies on an experimental mushroom unit were sampled simultaneously in both spawn-running and mushroom cropping-houses by sticky traps. Comparison between these populations showed that each reached a maximum about August and that the rate of increase, as measured by the ratio between them, varied from 22 × (at the beginning of February and in mid-August to 115 × (at the beginning of June and the end of December). Population growth within a crop was assessed from the peaks plotted from weekly catches. Three such peaks could be seen, starting from initial numbers which were high, on average, at casing but with little increase after the seventh week of cropping. However, population growth within crops, found by pooling data for different seasons, showed logistic increases though slopes varied from low, for May to June-spawned crops, to high for October spawning. Wide variations occurred in the proportion of the total flies represented in the initial catches in the first wk after casing. Partial regressions were examined for the numbers caught in cropping-houses on those taken in spawn-running rooms throughout the year. Catches for crops spawned during June to September gave lower slopes for high cropping-house populations. Spawn-running room catches showed a linear relation with outdoor 9.00 a.m. B.S.T. temperature and cropping-house numbers a logistic relation, a better fit obtaining with temperatures at spawning rather than 5 wk later during cropping. Catches during spawn-running were correlated with those during subsequent cropping and these with catches made during the previous crop on the unit, irrespective of site. Since it was bimodal, rate of increase between spawn-running and cropping-houses did not correlate with outdoor temperature but revealed some very high catches in winter. Many flies were trapped in the cropping-houses early in the year when flies were absent from spawn-running rooms. Evidence for movements within farms is discussed, especially with respect to overwintering of the phorid, which validates routine trapping of both populations.     

The Continuous Culture of Luminous Bacteria: a Luminostat

A method has been designed for the continuous culture of luminous bacteria. The control system for the culture uses a combination of luminescence and optical density as a light signal received by a photomultiplier. This combined signal operates pumps which exchange the growth medium. Using this method, a culture of brightly luminescing bacteria was maintained for periods up to 3 weeks.     

The phylogeny of the ant tribe Formicini (Hymenoptera: Formicidae) with the description of a new genus

Abstract. The holarctic ant tribe Formicini is revised, the new genus Bajcaridris described, and possible phylogenetic relationships are discussed. The subgenus Iberoformica is synonymized with Formica. A synopsis, diagnosis and keys to the genera are provided.