Relations of Cercospora beticola with Host Plants and Fungal Antagonists
Cerco pora leaf pot (CLS) cau ed by Cercospora beticola Sacc., is sti ll considered to be the mo t important foliar di ease of ugar beel. The di ea e ha been reported wherever ugar beet i grO\\ n (Bieiholder and Weltzien 1972). Since the di ease wa fir t identified. management of CLS of ugar beet has been an ongoing mi ion of plant pathologists. Toda}. everal trategie are available and applied either s ingly or in combination to manage the di ea e. The e management trategie , which were ummarized by Windels et al. (1998), include cultural practice uch a deep tillage, rotation with non-host crops and identification and elimination of econdary weed host . Other include breeding and use of re i.tant cultivars and application of fungicide. The u e of re i tant sugar beet cultivars has long been an integral pan of CLS management; however, problems associated with selection of re i tant cuhivars again t CLS are wel l documented and were recently reviewed by Weiland and Koch (2004). According to the author , resistance to CLS in sugar beet has been de cribed as quantitatively in herited and rate limiting with respect to disease development (Smith and Gaskill 1970, Ro i et a l. 1999). Although resistant cultivars have proven effective in both North America and Europe, they nonetheless exhibit low heritability (Smith and Ruppel 1974), and cultivar bred for Cercospora resistance can still exhibit leaf pots if climatic condition favorable for the disease occur.
Differentiation and Detection of Sugar Beet Fungal Pathogens Using PCR Amplification of Actin Coding Sequences and the ITS Region of the rRNA Gene.
The DNA sequences of the actin genes of several fungi were compared and highly conserved regions in the coding sequence were identified. Deoxyoligonucleotide primers were synthesized based on conserved sequence blocks in the 5' and 3' ends of the open reading frame encoding the actin protein. In addition, primers (internal transcribed spacer [ITS] regions 1 and 4) based on conserved regions of the ribosomal RNA (rRNA) genes of fungi were synthesized. Use of the primers in the polymerase chain reaction (PCR) resulted in the amplification of DNA products from the genomes of sugar beet fungal pathogens of a size consistent with the amplification of the actin gene and rRNA gene sequences, respectively, in these fungi. With one primer pair (5FWDACT and MIDREVACT) directed to the actin gene, the major products amplified from the DNA of Aphanomyces cochlioides, Pythium ultimum, Cercospora beticola, Phoma betae, Fusarium oxysporum, and Rhizoctonia solani were of the sizes of 0.9, 0.9, 1.1, 1.1, 1.2 and 1.7 kilobase pairs (kbp), respectively, whereas no product was generated from the DNA of sugar beet (Beta vulgaris L.). Restriction endonuclease digestion of products amplified using 5FWDACT and MIDREVACT permitted the differentiation of A. cochlioides from A. euteiches. Use of ITS1 and ITS4 in PCR reactions employing the same template DNAs and reaction conditions yielded single products of 0.7, 0.8, 0.5, 0.5, 0.6, and 0.7 kbp, respectively, as well as a 0.7-kbp product from DNA of sugar beet. The data indicate that actin and rRNA gene sequences are appropriate targets for the development of PCR-based strategies for distinguishing sugar beet fungal pathogens at the genus level. The presence of A. cochlioides DNA in extracts of diseased sugar beet seedlings was detected using PCR with primers 5FWDACT and MIDRE-VACT.
The Tsetse Problem on the Eastern Cattle Route in the Gold Coast
1. Primary fly-belts round Makongo consisted of three different vegetational communities: a Cynometra-Vitex association along the main length of the Makongo river, on a clay soil; a Ficus congensis association along the river close to the town, on a sandy soil; and Isoberlinia doka woodland on moist sandy soil north-west and south of Makongo. 2. Secondary fly-belts of less dense vegetation occur in the orchard bush savannah round Makongo, and these are not colonised until the commencement of the rainy season. 3. Glossina tachinoides and G. palpalis both occurred in the riverside communities, and G. palpalis alone in the Isoberlinia woodland. 4. Along the river G. palpalis outnumbered G. tachinoides by 3:1 in the dry season. At the commencement of the rains G. tachinoides increased more quickly than G. palpalis , bringing their numbers very nearly equal, but at the end of the rains there was a decrease in G. tachinoides which restored the original proportion. 5. G. morsitans had been found at Makongo formerly but was not met with at the time of this investigation, its absence being due to the disappearance of the larger antelope from the neighbourhood. 6. Smaller game animals, small mammals and reptiles afforded an adequate food supply for tsetse in the fly-belts, and also passing herds of cattle, as well as natives from the village and travellers. 7. The distribution of G. palpalis within the fly-belts was markedly influenced by the proximity of a cattle road along which herds of cattle passed almost daily, and by village water-holes. 8. During the dry season the primary foci were always found to be the places of greatest relative humidity, and the fly does not tend to move out of these until the general atmospheric humidity has reached a certain fairly high degree. 9. In clearing the fly-belts the removal of all primary foci within a quarter of a mile of the town and of thick bush within 100 yards of water-holes was undertaken. The work lasted from the beginning of February to the end of March 1931. 10. The effect of clearing the Isoberlinia doka woodland was to banish G. palpalis completely, and it never returned to these clearings. 11. On clearing the riverside Ficus congensis fly-belt, G. tachinoides was practically eliminated for the first three months, but reappeared in the clearings in June when there was a general increase and up-stream migration of this fly. G. palpalis remained in this clearing in fluctuating numbers up to June, when observations were suspended. 12. 565 marked tsetse were liberated in the fly-belts immediately previous to clearing. Of G. palpalis 12·7% were recaptured in the clearings and 11% outside the clearings. Of G. tachinoides 5·5% were recaptured in the clearings and 6·8% outside.