Interplot Interference Research Articles

Does interplot interference affect the screening of wheat for yellow rust resistance?

In small plots, adjacent to one another, a representational error can be expected when screening for quantitative forms of resistance to airborne pathogens. The representational error or interplot interference may occur as an underestimation of the level of resistance and/or as an error in the ranking of the entries tested.

Effect of crop age on primary gradients of late leaf spot (Cercosporidium personatum) on groundnut

Artificial sources of late leaf spot were established by inoculation of one plant at the centre of several groundnut plots differing in age. First-generation dispersal and resulting primary gradients of disease were then compared. The gradients were corrected for source strength, spontaneous infection (primary gradient), and interplot interference (first-generation dispersal). The shapes of the gradients for spore dispersal and of the gradients of disease corresponded for each age of groundnut plot, but differed between the ages. The slopes of gradients were steeper in the older plots. Spore dispersal and the resulting disease gradients were not isodiametric, gradients being most protracted in a north-to-north westerly direction. The results suggest that the strength of the sources was reduced by abscission of infected leaves in the sources of the younger plots, whereas accessibility of the canopy to the transported spores was reduced by increasing canopy density in the older ones.

Modelling the Diffusion Component of Dispersal During Recovery of a Population of linyphiid Spiders from Exposure to an Insecticide

This study was designed to describe the spatial and temporal dynamics of an assemblage of linyphiid spiders during recovery from local depletion by an insecticide. A field of winter wheat was partly sprayed with log a.i. ha-' of deltamethrin. Of the linyphiid spiders, Erigone atra (Blackwall) was reduced by 89% and Oedothorax apicatus (Blackwall) females by 82%. Recovery of the populations is described in space and time by comparisons of relative densities of spiders at different distances from an adjacent unsprayed area using multiple-range tests, regression models and a diffusion model. Median estimated recovery times (ERT50) are calculated for species at different distances from the unsprayed area. For 0. apicatus females ERT50 ranged from 1.1 to 15*3 weeks and for E. atra from 3-7 to 6*5 weeks at 15 and 75m from the unsprayed area. Differences in recovery patterns for three spider categories are explained in terms of susceptibility to the pesticide and modes of dispersal. The consequences are discussed with reference to interplot interference in field ecotoxicity trials and commercial practice. Key-words: Deltamethrin, diffusion, dispersal, interplot interference, linyphiid spiders, modelling, spatial dynamics

Race-specific aspects of partial resistance in wheat to wheat leaf rust, Puccinia recondita f.sp. tritici

Partial resistance (PR) in wheat to wheat leaf rust (Puccinia recondita f.sp. tritici) is characterized by a slow epidemic build-up despite a susceptible infection type. Two greenhouse tests and two field tests, in which 11 spring wheat cultivars were exposed to five wheat leaf rust races, revealed some indication for race-specificity of PR. In the greenhouse, the expression of PR was highly dependent on the environment. Significant cultivar-race interactions in the first experiment were lost in the second experiment probably due to cultivar-environment and cultivar-race-environment interactions. In the polycyclic field tests several factors played a role in explaining the inconsistency of the cultivar-race interactions, such as differences in initial inoculum, genotypic differences in earliness, interplot interference or environmental conditions. One cultivar-race combination showed a significant but small interaction towards susceptibility in both field experiments. The interaction was probably too small to detect in the monocyclic greenhouse tests. The results do not conflict with the idea that a gene-for-gene relationship could exist between PR-genes in the host and genes in the pathogen. Some problems with regard to the selection of PR in wheat to wheat leaf rust are discussed.

Rice crop loss from insect pests in wetland and dryland environments of Asia with emphasis on the Philippines

Yield losses from insect pests were determined by the insecticide check method in 60 crops in the Philippines from 1976–1986 in three rice environments with traditional and modern cultivars in 10 sites. Plot size of 100 m2 minimized interplot interference from insecticide protection on untreated plots. Low and high crop losses were recorded across sites in drylands (2-39%, -X = 25%), rainfed wetlands (13-24%, -X = 21%), and irrigated wetlands (5-40%, -X = 18%). Weighted crop loss for the Philippines based on production by environment and cultivar type averaged 18.3% or 0.57 t/ha per crop. Consistently greater yield loss occurred in the vegetative (50%) than reproductive (30%) or ripening (20%) stages across environments and cultivars. No epidemics affected the trials therefore crop losses were those from chronic pests. The major chronic pests in the wetlands were stem borers, leaffolders, whorl maggot, and rice bug; and in the drylands were ants, seedling maggots, white grubs, leaffolders, stem borers and rice bug. Yield loss variability was greater between fields than crops or sites, therefore a control strategy based on corrective actions when pest numbers reach threshold levels is more efficient than prophylactic actions. Yield loss was more in early maturing cultivars stressing the importance of compensation in tolerating insect damage. Insect stresses perhaps can be compensated by total crop management to increase the plant’s ability to tolerate insect damage.

Interplot Interference in Field Plots with Leaf Rust of Maize

Abstract Interplot interference, or the influence of one host genotype on another when grown in adjacent plots, can be a problem with the evaluation of partial resistance to airborne pathogens. Moreover, interplot interference may affect selection in the plant breeding nursery. To estimate the degree of interference in a typical sweet corn (Zea mays L.) breeding nursery, the partial resistance of 3 hybrids grown in several field plot treatments was examined. Treatments consisted of differing spatial arrangements of the 3 hybrids. In a 2-year study, mean rust level differed significantly for 5 field plot treatments. As the potential for leaf rust increased, the ability to distinguish between hybrid disease reaction diminished. In addition, the variability in disease reaction was reduced as rust potential increased for hybrid and field plot treatment, indicating that when high levels of leaf rust existed, disease gradients tended to flatten.

Interplot interference and the assessment of barley cultivars for partial resistance to leaf rust, Puccinia hordei

The barley cultivars Akka, highly susceptible, and ‘Vada’, partially resistant to barley leaf rust, Puccinia hordei, were evaluated for the amount of leaf rust in five experimental field plot situations over three successive years. The field plot situations were: A) plots well isolated from each other by distance and non-leaf rust contributing host plants; B) adjacent plots of 4×41/2 m (18 rows); C) adjacent plots of 4×11/2 m (6 rows); D) adjacent plots of 4×1/4 m (1 row); E) adjacent plots of only one plant (cultivar mixtures). The sporulating leaf area of each plot was measured from samples of 20 tillers taken at random from each plot. In each year the difference in sporulating area between ‘Akka’ and ‘Vada’ was large to very large in the absence of interplot interference in the isolated plots, ranging from 150 to 2100 times. In the adjacent plots the partial resistance of ‘Vada’ was greatly underestimated, 5 to 16 times in the situation B, 14 to 30 times in C, and 75 to 130 times in D and E. Testing lines or cultivars in adjacent plots is the standard procedure in use in breeding programs and in tests of cultivars for their agricultural value. To avoid such under estimation the following procedure is suggested. A few cultivars representing the known range of partial resistance and whose level of partial resistance is well known are evaluated together with the lines and cultivars whose partial resistance has to be assessed. This is demonstrated with a number of cultivars of which resistance values are know from the recommended variety lists for England and Wales. Cultivars have been assessed in Wageningen over four years together with the check cultivars Akka, Sultan, Julia and Vada representing the range of partial resistance with values (on a 1 to 10 scale) of 1, 3–4, 7 and 8 respectively, based on isolated plots experiments.

Negative Interplot Interference in Field Experiments with Leaf Rust of Wheat

Negative Interplot Interference in Field Experiments with Leaf Rust of Wheat

The assessment of crop losses in cereals

The reasons for assessing crop losses due to pests of cereals are reviewed; for making decisions in pest management based on costs and benefits, for allocating resources on the most important pests, and as a guide to how yield is lost. Crop yield is seen as a balanced system, with inputs and output. The methods of quantifying pest attack, measuring losses and the difficulties met are discussed: the interaction of losses, interplot interference, mixed crops, loss distribution and crop compensation. Surveys of loss are described, with examples.

Pathogenic variability of downy mildew (Sclerospora graminicola) on pearl millet. II. Statistical techniques for analysis of data

SUMMARYDifferent cultivars of pearl millet were exposed to infection by asexual propagules of Sclerospora graminicola in Polythene tunnels. Subsequent incidence of disease was measured on one‐month old seedlings. The data consisted of binomial proportions based on differing total numbers of seedlings. It is shown how to utilise the logit link in the GLIM statistical package for analysis to compare variety performances. In addition the possibilities of interplot interference and intraplot variation were investigated using GLIM. Interplot interference occurred infrequently and did not affect the rank order of the cultivars in terms of their response to the fungus infection. Intraplot variation was also shown to be non significant in spite of proximity of some plants to the disease spreader plants. Once these potentially confounding phenomena were eliminated the cultivars could be compared directly with impunity. GLIM was also used to confirm that the type of symptom expression was a stable feature of each host genotype.

Crop losses: The need to quantify the effects of pests, diseases and weeds on agricultural production

Crop losses caused by pests, including rodents and birds, and by diseases and weeds, are defined, and previous studies reviewed. Information about losses is needed to monitor the effects of pests and diseases on crop production, in individual countries and worldwide, important for food policy and economic reasons; to make decisions and allocate resources on the study, management and control of pests and diseases; to stimulate action against them; to provide guidelines for research on crop improvement to prevent pest and disease attack; and as a basis for judgement on the importance of pests, diseases and weeds in relation to agriculture and the environment. The causes of such losses, why information must be up to date, and methods of assessing pests, diseases, weeds and losses are examined. The part played by losses in the development and use of economic pest and disease control action thresholds is discussed, including pest, disease, crop, climatic, economic and farmer attitude factors. The types of relation between yield and pest and disease attack are reviewed, how to measure the relation in practice, how to obtain different amounts of attack, surveys of losses, and the difficulties met in the study of losses: interaction; compensation; interplot interference; variation; and distribution. Sources of information on world losses, training and the work of the FAO are reviewed. General guidelines on crop loss assessment are given.

Interplot Interference: A Model for Planning Field Experiments with Aerially Disseminated Pathogens

Interplot Interference: A Model for Planning Field Experiments with Aerially Disseminated Pathogens

Interplot Interference in Field Experiments with Late Blight of Potato (Phytophthora infestans)

Interplot Interference in Field Experiments with Late Blight of Potato (Phytophthora infestans)