SUMMARYThe influence of pH on the growth of, and carbohydrate utilization by, three ectomycorrhizal fungi in culture was assessed by growing them on glucose, sucrose and raffinose in the presence and absence of 0-05 .M phosphate buffer and 0-05 . M 2-(N-morpholino) ethane-sulphonic acid buffer (MES). This concentration of phosphate significantly inhibited growth of Cenococcum geophilum and Rhizopogon roseolus on all carbon sources. Suilius bovinus was more tolerant, exhibiting uninhibited growth on glucose, though adaptive growth on both sucrose and raffinose was significantly less in phosphate buffer than in the other two systems. MES had a superior buffering capacity and was less inhibitory to growth of the three fungi than phosphate buffer. Tbe growth of C geophilum on all carbon sources was uninhibited in MES, although this buffer significantly inhibited adaptive growth by the other two species on sucrose and raffinose, possibly by inhibiting induction or activity of invertase. The use of phosphate bufFers by several workers in tests of carbohydrate utilization by ectomycorrhizal fungi will undoubtedly have affected their growth. This may, to some e.\ tent, explain differences in patterns of utilization of carbon between isolates of the same species which have been reported by different investigators. These have previously been attributed to variability between strains in utilization of carbohydrate rather tban in sensitivity to phosphate. Possible ways by which phosphate inhibits growth are discussed.
The potato flea beetle species Epitrix similaris and Epitrix cucumeris were identified in mainland Portugal in 2009. This was the first finding of the species E. similaris in the EPPO region, and the first report of the species E. cucumeris, established in the Atlantic Islands of Azores (Portugal) for three decades, in the mainland EPPO zone. Preliminary information on the damage patterns caused by E. similaris and E. cucumeris on potato and their host plant preferences is provided. Leaf feeding by the adults causes the characteristic shot-hole pattern common to flea beetles. The larvae of both species develop on the root system and cause damage to the tubers. In field experiments, tuber damage by E. similaris presented three patterns: superficial tracks (serpentines), black splinters, and shallow holes. In the laboratory E. cucumeris was observed to be able to feed on very small immature tubers, causing serpentines and holes as well. However, in some cases it developed exclusively on roots. The adults of both Epitrix species hardly fed and reproduced on sweet pepper plants but fed and reproduced on the remaining five solanaceous plants tested (aubergine, Datura stramonium, tomato, potato and Solanum nigrum). E. similaris produced a much higher number of progeny on potato and on S. nigrum than on the other host plants. E. cucumeris produced more offspring on S. nigrum than on the other host-plants.
Epitrix tuberis and E. cucumeris are major pests of potatoes in North America. E. tuberis causes the most serious damage because the larval feeding can cause superficial serpentine tunnelling on the surface of tubers as well as deeper pits. This damage can make crops unmarketable. By contrast, E. cucumeris mainly damages the foliage, and yield losses can occur when the adults reach high densities. In 2004, potato tuber damage characteristic of E. tuberis was seen in Portugal. In 2008, damage was more widespread and severe. E. cucumeris and a lesser known species, E. similaris, were recorded in affected fields. E. similaris has since been found across Galicia, Spain. E. similaris is thought to be the most likely cause of the tuber damage in Portugal, but it is possible that E. cucumeris or an as yet undetected Epitrix species is causing the damage. In 2010, a pest risk assessment for the Euro-Mediterranean area identified the movement of adults and pupae with seed or ware potatoes and associated soil as being the highest-risk pathways for the spread of Epitrix. In 2012, EU emergency measures were agreed to reduce the risk of further introductions and the rate of spread of these pests.
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