Annals of Applied Biology

The air in several Jamaican banana plantations was sampled from July 1960 to September 1961 with an automatic volumetric spore trap. In dry weather, many fungi showed typical diurnal periodicity. Group I fungi (Deightoniella, Nigrospora, Cordana, Corynespora, Zygosporium and Zygophiala) first appeared shortly after 06.00 hr., reached a peak before 09.00 hr. and then showed a rapid fall. Group II fungi (Cladosporium, Alternaria, Curvularia, Cerebella, Pithomyces, Periconiella, Memnoniella, Ustilago and others) and pollens had peak concentrations between 09.00 and 14.00 hr. Groups I and II formed the majority of the spore catch during daylight, but they were practically absent between 20.00 and 06.00 hr. Group III fungi (represented chiefly by ascospores, especially of Leptosphaeria spp., basidiospores and splash‐dispersed types) first appeared near 20.00 hr., attained a maximum between midnight and 06.00 hr. and a minimum during daylight. In dry weather, Cladosporium conidia accounted for 23% of the total catch; coloured fusiform spores for 18%; coloured basidiospores for 16%; unclassified minute spores (including Sporobolomyces) for 14%; and Deightoniella only 0.2%.

During rain, the typical dry‐air‐spora decreased and was replaced to varying extents by group III ascospore types and splash‐dispersed spores. When, after rain, the plantation dried out during daylight, group III fungi decreased while groups I and II briefly reappeared before the typical night‐time flora developed. When rain was continuous during daylight, groups I and II were rare; ascospores and splash‐dispersed spores dominated the traces. All fungi occurred in low concentrations during heavy rain, periods of drought and strong wind. With rain or under‐tree irrigation or both, the following days had varying increases of all group I fungi and certain group II fungi, probably because favourable humidity conditions caused increased sporulation.

Observations were made on the effects of reduced rates of herbicide and nitrogen on naturally occurring populations of Viola aruensis. Progeny arising from these plants were grown in a uniform environment and monitored through to maturity. The size and number of reproductive structures produced by the maternal plants were positively correlated with the maternal plant weight. Herbicide dose affected the plant height of offspring and the effects were more pronounced in those from plants which had received 160 kg N ha^‐1than 40 kg N ha^‐1. Although the maternal effects on offspring size diminished with time, the number of reproductive structures in the offspring was significantly correlated with plant height during early development. Increased nitrogen availability to the maternal plant in the absence of herbicide may therefore increase the overall productivity of the subsequent generation.

The final yield of a crop is the product of growth during the growing season and a number of developmental processes occurring throughout the life cycle of a crop, with most genes influencing the final outcome to a degree. However, recent advances in molecular biology have developed the potential to identify and map many genes or QTLs related to various important traits, including yield, plant adaptation and tolerance to stresses. Significant G×E interactions for yield have been identified, as have interactions associated with QTLs for yield. However, there is little evidence available to confirm that a QTL for yield from a parental line in one mapping population may improve yield when transferred into an adapted, high‐yielding line of another population. In order to narrow the apparent gap between the genotype and the phenotype with regard to yield, it is important to identify key traits related to yield and then attempt to identify and locate the genes controlling them. The partitioning of the developmental time to anthesis into different phases: from sowing to the onset of stem elongation and from then to anthesis, as a relatively simple physiological attribute putatively related to yield, is discussed. If the relationship holds in a wider range of conditions and the genetic factors responsible are located then the genetic basis of yield should be identified. There has also been significant progress in crop simulation modelling. Using knowledge of crop physiology and empirical relationships these models can simulate the performance of crops, including the G×E interactions. Such models require information regarding the genetic basis of yield, which are included in the form of genetic coefficients. Essentially models are constructed as decision‐making tools for management but may be of use in detecting prospective traits for selection within a breeding programme. Problems associated with this approach are discussed. This review discusses the need to use crop physiology approaches to analyse components of yield in order to reliably identify the genetic basis of yield.

A yam potyvirus was isolated from Dioscorea alata samples collected in Nigeria. The virus was not transmissible mechanically but was transmitted by Aphis craccivora to four cowpea cultivars (Ife Brown, IT84S‐2114, IT82E‐10 and TVu2657), and from which it could be mechanically transmitted between the cowpea cultivars. In infectivity‐ tests using cowpea extracts, the virus had a dilution end point of 10^‐4, a thermal inactivation point of 60–65°C and longevity in vitro of 2 days at room temperature. The virus coat protein had an estimated molecular weight of 32 100 daltons. The virus was identified as an isolate of Dioscorea alata virus (DAV; syn. yam virus 1) due to its biological characteristics and its serological reaction with antiserum raised against DAV. The virus is not related to yam mosaic virus, but distantly related to blackeye cowpea mosaic virus and cowpea aphid‐borne mosaic virus.

In experiments on the infection of bee larvae with Nosema apis, the parasitic spores did not germinate and infected adults did not result. In hives of bees infected with N. apis about 10–20% of the eggs laid did not complete their development probably because of inadequate care and feeding.

Soil‐borne viruses of the tobacco‐rattle type occur in sandy and peaty soils in many parts of Scotland, and infect many species of crop and weed plants, often only in the roots. They also occur in potato plants that have diseases of the stem‐mottle type. The viruses can be distinguished from other soil‐borne viruses occurring in Britain by the symptoms they cause in tobacco, Chenopodium amaranticolor and French bean.

Some virus cultures (M types) multiplied readily and were easily transmitted by mechanical inoculation, whereas others (NM types) were transmitted mechanically only with difficulty. The behaviour of NM types remained constant during twenty successive subcultures. Only slight differences were noted between the symptoms caused by M and by NM types. A proportion of the single‐lesion isolates made from cultures of the M type behaved in every way like NM types: this proportion differed with different parent cultures. Single‐lesion isolates that were of the M type mostly caused somewhat different symptoms from their parent culture. All M types that were tested, including one from the Netherlands, were serologically related: however, different cultures, and different samples of the same culture propagated on different occasions, varied in antigenic constitution. Belladonna mosaic virus, described by Smith (1943) from England, was serologically related to tobacco rattle virus. Infection with each of several M types (including the Dutch culture), protected Nicotiana sylvestris plants from the effects of each of the others. NM types also protected N. sylvestris from the effects of the Dutch culture, but the latter was subsequently isolated from the tip leaves of such plants. Sap from plants infected with cultures of the M type contained characteristic rod‐shaped particles, but none was seen in sap from plants infected with NM types.

In tobacco sap, M types had the following properties: thermal inactivation point, 80–85°C.; dilution end‐point, 10^‐5‐10^‐6; longevity in vitro, over 6 weeks; infectivity survived freezing and precipitation by ammonium sulphate, but not exposure to pH 3. In many of its properties, including the unusual one of failing to show photoreactivation after ultra‐violet irradiation, tobacco rattle virus resembles tobacco mosaic virus.

Soil‐borne viruses occurring in Britain are classified into three groups, exemplified by tobacco necrosis, tomato black ring and tobacco rattle viruses.

A technique has been developed for the rapid determination of some species of prey consumed by mites and insects. The method detects prey enzymes within the gut of a predator by polyacrylamide gradient gel electrophoresis and subsequent staining for esterase activity. It is sufficiently sensitive to detect fruit tree red spider mite (Panonychus ulmi) esterases within the gut of a single predacious mite (Typhlodromus pyri) for at least 31 h after feeding. The method has been used to demonstrate feeding relationships among a range of insect and mite predator and prey species in the laboratory and in the field.

The expansion and persistence of leaves of sugar beet (Beta vulgaris) were measured in a series of crops grown in five seasons between 1978‐82 to establish how their growth varied between seasons, was affected by certain agronomic treatments and contributed to changes in leaf area index. Thermal time (accumulated temperature above 3°C) rather than days from sowing was used as a basis for comparing growth in different seasons.

Leaf size depended on position on the stem and was influenced by sowing date, nitrogen fertiliser rate, plant population and the development of crop water stress. Changes in size were mostly associated with changes in the rates, rather than the duration, of expansion. When compared across seasons, the rate and duration of expansion of individual leaves were strongly negatively correlated so leaf size tended to be a more stable characteristic than either of its determining components. Nevertheless, final leaf areas varied by as much as 20% between seasons and this variation was attributable more to the temperatures experienced by leaves prior to unfolding and to the amounts of nitrogen present in the shoot at that time than to conditions during the main period of leaf expansion.

Four methods were compared for inoculating red clover with selected mycorrhizal fungi when sown in a field containing an indigenous mycorrhizal population. The largest amount of mycorrhizal infection (around 65% of root length infected) was obtained by placing inoculum with the seeds in furrows. The inoculum used was standard soil inoculum from stock plant cultures spread by hand or the same inoculum concentrated to about one seventh by wet‐sieving, and then fluid‐drilled. The effectiveness of multiseeded pellets (seeds stuck onto pellets of soil inoculum) applied broadcast was more variable, infection ranging widely around an average of 30%. Applying both soil inoculum and seeds broadcast produced just under 10% infection, similar to that in the controls given autoclaved inoculum. Seedling establishment, in contrast, was‐better where seeds were applied broadcast than in furrows. It seemed therefore that multiseeded pellets might be the best compromise for achieving reasonable infection in most plants, but fluid drilling had the advantages of greatly reducing the amount of inoculum needed and of readily combining seeds and inoculum in a single carrier.

Wild rice Zizania latifolia is a perennial emergent aquatic plant widely distributed across China. Wild populations of Z. latifolia are important to aquatic ecosystems and are valuable genetic resources for breeding. However, they have been faced with significant habitat losses in recent decades. For 10 nuclear microsatellites, high levels of genetic diversity (H_E = 0.572–0.636) were found across seven surveyed populations from central China. The main factors responsible for that were its long life history and predominant outcrossing reproductive system. Low genetic differentiation among populations was found based on Wright's F_ST = 0.098. Similarly, AMOVA analysis showed only 7.73% of the total molecular variation was attributed to inter‐population differentiation. The weak population structure of Z. latifolia could be due to high gene flow mediated by water or birds (Nm = 2.30, M = 2.18). Importantly, most populations exhibited mutation‐drift disequilibrium, suggesting a recent population decline. Based on the results, wild populations of Z. latifolia are expected to lose genetic diversity and increase genetic structure in future generations. Therefore, conservation management is urgently needed to maintain the genetic resources of Z. latifolia.