The behaviour of potato mop-top virus in soil, and evidence for its transmission by Spongospora subterranea (Wallr.) Lagerh.

Potato mop-top virus (PMTV) was best detected in field soils by air-drying them for more than a week before remoistening and growing seedlings of Nicotiana tabacum or N. debneyi for a 6–10 week period. Infection of N. tabacum was assessed by inoculating sap from roots and shoots to Chenopodium amaranticolor. Similar inoculations from N. debneyi were far less convenient for detecting PMTV than recording leaf symptoms, but slightly more efficient. Air-dry soil retained PMTV infectivity for 9 months, when passed through a 50 μ sieve or when diluted with 10³ but not 10⁴ parts of steamed soil. Tobacco seedlings were not infected when their roots were steeped in PMTV-containing tobacco sap. Infective soils contained Spongospora subterranea, spore balls of which resisted air-drying for more than a year and passed a 50 μ sieve. Roots of susceptible seedlings were infected with PMTV when exposed to spore balls of S. subterranea taken from powdery scabs on PMTV-infected potato tubers, or to suspensions obtained by steeping, in nutrient solution, roots infected with virus-carrying cultures of S. subterranea. Plants in several families were hosts of S. subterranea, but probabilities of infection when exposed to spore balls differed greatly between families and only species of Solanaceae were good hosts. The ten species infected with PMTV when grown in infective soil or when exposed to spore balls of S. subterranea taken from PMTV-infected potato tubers are all members of this family. PMTV seems to be carried internally in S. subterranea spore balls and survived in them for at least a year. PMTV was transmitted by S. subterranea to Arran Pilot potato, causing yellow blotches in some leaves and spraing in many tubers. However, when newly infected with PMTV in the field, not all Arran Pilot tubers developed spraing. Also, although many spraing-affected or symptomless but PMTV-infected tubers carried PMTV-containing spore balls of S. subterranea, powdery scabs were rarely found near the centres of the rings of primary spraing. PMTV became established in virus-free soil when PMTV-infected tubers carrying S. subterranea were planted as ‘seed’ but not when virus-free tubers bearing powdery scabs were used. 5. subterranea seems the main, and possibly the only, vector of PMTV in the soils examined. S. subterranea did not transmit potato aucuba mosaic virus from potato to N. debneyi or Capsicum annuum.     

The morphology of the sphaeromatid brood pouch (Crustacea: Isopoda: Sphaeromatidae)

The structure of the brood pouch and mouthparts of ovigerous female sphaeromatids is described. Taxonomically, these are shown to be important generic characters and some attempt is made to relate structure to function. Expanded maxillipeds (which produce a current of water through the marsupium) are shown to occur only in genera which have oostegites overlapping in the mid-line and reaching the mouthparts anteriorly. The reduction of the mouthparts of some genera cannot be explained, but it may conserve energy at the final moult. No platybranchiate genera (subfamily Cassidininae) have the mouthparts reduced but some have the maxilliped expanded. Some correlation between brood pouch structure and habitat is suggested. Genera with a brood pouch composed only of oostegites (and hence liable to disruption by turbulence and particle abrasion) occur sublittorally or, if intertidal, adopt a protected, crevice dwelling habit. Genera with a brood pouch composed of large opposing pockets (which are more able to resist disruption) occur intertidally or in shallow water, and may be found in wave-washed sand. Some wood-boring species of the genus Sphaeroma Latreille show a reduced number of oostegites when compared with non-boring species. This presumably relates to their burrowing habit.     

Host/parasite relations up to the time of tuber initiation in potato plants infected with Verticillium spp

The growth pattern of potato plants, infected with V. albo-atrum and V. dahliae, was studied, using growth-analysis techniques, during the initial stages of development up to tuber initiation. During the first 5–6 weeks of growth the morphology of the infected plants was not affected, but the distribution of dry weight materials between various plant organs and the growth rates of the whole plants were affected much sooner. In contrast to healthy plants, those infected exhibited lower specific leaf areas, higher leaf weight ratios and higher leaf area ratios, and, under dry conditions, lower relative growth rates and lower unit leaf rates. Thus during the incubation phase of the disease, although effects of infection are not immediately apparent, Verticillium pathogens have a considerable influence upon the development of the host.     

Effect of main stem number and lateral stem development in potato plants infected with Verticillium albo-atrum and V. dahliae

‘Early-dying’ disease was examined in potato plants (King Edward) with varying numbers of main stems and lateral stems. Infection with Verticillium affected neither the number of main stems produced nor the stem number/ lateral number/yield inter-relationships, but did slightly reduce lateral development. The host growth pattern, however, markedly influenced the severity of disease: infected plants with a single main stem or a few, compared with those having many main stems, showed delayed symptom expression and also produced many laterals which further reduced disease severity and increased longevity. Thus yield reductions as a result of infection are likely to be smaller in single-stemmed plants showing considerable lateral development than in those plants with many main stems and few or no laterals.     

Association of mycoplasma-like bodies with potato witches' broom disease from Scotland

Mycoplasma-like bodies were found by electron microscopy of sections of sieve tubes, both from shoots and roots of potato (Solanum tuberosum) plants affected by Scottish witches' broom disease and from graft-inoculated tomato shoots. The bodies were bounded by a unit membrane, contained ribosome-like material and mostly measured 200–800 nm in diameter. Most were oval in cross-section but some had lobes or slender protrusions. Some of the bodies were found in the mouths of sieve pores.     

西双版纳地区钝叶榕的物候变化规律

钝叶榕是西双版纳地区分布广泛的一种榕树(雌雄同株),具有较为特殊的传粉体系。近三年的野外物候观测数据显示,钝叶榕个体绝大多数每年结果1~2次,极少数一年结果3次,通常在雨季增加结果次数,出现树内异步的现象。钝叶榕结果树内同步,树间异步。钝叶榕雌花期和雄花期不能很好吻合,榕蜂系统在观测范围内处于不稳定状态,导致钝叶榕的雌花期和雄花期比其它种类的榕树长很多。结果表明：钝叶榕结果物候可能受相对湿度影响最大,但总体上其物候与温度、降雨量和相对湿度的相关关系未呈现明显的规律性。钝叶榕的物候变化应受其它气候因子作用或是各种生物因子和非生物因子共同作用的结果。物候和气候的现象十分复杂,进一步对钝叶榕物候的不同方面和各种气候因子进行相关性分析十分必要。     

Host range, vector relations and serological relationships of cotton leaf curl virus from southern India

In 1989 to 1991, leaf curl disease was observed in cotton (Gossypium bar-badense cv. Local) grown in kitchen gardens in five districts in Karnataka State, India, and in 1994 it was recorded in G. hirsutum cv. Sharada in two districts. Symptoms consist of leaf curling, vein thickening, leaf enations, and stunting and distortion of plants. The disease is caused by cotton leaf curl virus (CLCuV-K), which was transmitted by the whitefly Bemisia tabaci to 24 plant species in six families. Hosts include bean (Phaseolus vulgaris), pepper, tobacco, tomato and several weeds, almost all of which developed leaf curl, with or without vein thickening. CLCuV-K was transmitted from cotton to cotton by adult B. tabaci after an acquisition access period of 1 h, could be inoculated in 5 min, had a minimum latent period of 8 h and was retained by viruliferous insects for up to 9 days. Female B. tabaci transmitted more frequently than males. CLCuV-K is a whitefly-transmitted geminivirus. It reacted with two out of 17 monoclonal antibodies (MAbs) raised to African cassava mosaic virus and five out of 10 MAbs raised to Indian cassava mosaic virus. CLCuV-K isolates from different locations in Karnataka had similar epitope profiles. As judged by these profiles, CLCuV-K is closely related to Indian tomato leaf curl virus from Karnataka, is distinguishable from several other whitefly-transmitted geminiviruses found in India and is still more distantly related to those, including cotton leaf crumple virus from the USA, found in other continents. CLCuV-K infected all cultivars tested of G. barbadense and one of six cultivars of G. hirsutum but none of G. arboreum or G. herbaceum.