K. Phelps

Investigating trends in vegetable crop response to increasing temperature associated with climate change

Abstract A thermogradient tunnel, 8.6 m wide and 31.9 m long, generating temperatures ranging from ambient at one end to ambient plus approximately 4 °C at the other, was used to assess the potential impact of increased temperatures associated with global warming on the growth of Iceberg lettuce (Lactuca sativa L.), leek (Allium ampeloprasum L.) and Roscoff cauliflower (Brassica oleracea var. botrytis L.) crops. Optimum mean temperatures for head weight in Iceberg lettuce and trimmed weight in leeks were identified as 12 °C and 15.7 °C, respectively, corresponding to temperature rises of 2 °C and 2.4 °C above the average ambient temperature during the experiments. Increased temperatures gave consistently earlier maturity of lettuce, delayed cauliflower curd initiation by up to 49 days and increased the final number of leaves in cauliflower by 36. The implications of these effects are discussed in relation to global warming.

Testing a vernalization model on field-grown crops of four cauliflower cultivars

SummaryData from a series of transplantings of four cultivars of summer-autumn cauliflower, grown on two sites, were used to test the accuracy of prediction of the timing of curd initiation, using a model of vernalization in cauliflower developed for cv. White Fox. This model was started at different numbers of leaves between 16 and 22, to simulate the end of juvenility at different stages of growth. Prediction of curd initiation was most accurate with juvenility ending at different mean numbers of leaves in each cultivar: White Fox 17.0, Dok Elgon 17.5, Revito 20.5 and White Rock 21.0. The intensity of the vernalization stimulus appeared to be similar for all cultivars.

INITIATION OF EARLY SUMMER CAULIFLOWERS IN RESPONSE TO TEMPERATURE

SummaryTwo experiments were conducted with the early summer cauliflower cvs Perfection and Gypsy. The first was in controlled environment cabinets with nine temperatures ranging from 6.3 to 22.88C. The second was in the field with three planting dates and plants grown with and without fleece cover. The experiment in controlled environments enabled a model to be developed which predicted changes in apex development through both the juvenile and curd induction phases. Both the end of juvenility and curd initiation were defined in terms of apex diameter. For cv. Perfection these were respectively 0.25 and 0.55.mm while with cv. Gypsy they were respectively 0.27 and 0.51.mm. The number of leaves produced at the end of juvenility was very different in the two experiments. When applied to the field temperatures from planting, the model predicted the end of juvenility early and therefore estimates of curd initiation were inaccurate. However, when the model was started, with the recorded apex diameter exceeding t...

Predicting frequency distributions in crops of carrot (Daucus carota L.) and red beet (Beta vulgaris L.)

SummaryAbility to predict variation in individual storage root size is essential as most root vegetables are marketed in diameter grades. There are, however, few methods that allow variability in size to be predicted. This paper describes a method for carrots and red beet, which uses a normal frequency distribution of the logarithm of each root weight plus a constant. The parameters of this distribution were relatively constant, or well correlated with the mean weight for several carrot and red beet data sets. This simple model was tested on independent data sets and there was a close agreement between observed and predicted yields in weight grades for carrots. Predictions for yields of grades of commercial interest were little affected by changes of 10% in the values of the parameters. In red beet, the independent data had been graded for diameter. Using weight grades corresponding to the diameters, a close prediction for yields in each grade was found. Thus, models that can predict mean weight of a carr...

Variation Studies in Carrots as an Aid to Breeding. VI. Genotype-Environment Interactions in Contrasting Field Environments

SummaryTwo series of field trials of carrot cultivars were conducted over the period 1968–73. In one series cultivars were grown at different sites and densities, repeated over years (the between-sites set), whereas in the second series similar cultivars were grown at a single site with different sowing dates, lengths of growing season and densities repeated over years (the within-site set). In each of the characters reported, namely yield, percentage of split roots, percentage of purple-topped roots and root length/diameter (LD) ratio, genotype χ environment (GE) interactions were detected within both environmental sets. An extension of joint regression analysis was used to estimate the relative linear responsiveness to environment of the cultivars and to test the consistency of these estimates over the two environmental sets. Conclusions differed somewhat between characters; for yield the largest interactions were non-linear, but some evidence of small linear interactions consistent over the two sets wa...

A Method for Ascertaining and Controlling Representation Bias in Field Trials for Airborne Plant Pathogens

The basic premise of running a field trial is that the estimates of treatment effects obtained are representative of how the different treatments will perform in the field. The disparities between the treatment effects observed experimentally, and those that would be observed were the treatments applied to the field, we term ‘representation bias.’ When looking at field trials testing the efficacies of treatment sprays on plant pathogens, representation bias can be caused by positive and negative inter-plot interference. The potential for such effects will be greatest when looking at pathogens that are dispersed by wind. In this paper, a computer simulation that simulates plant disease dispersal under such conditions is described. This program is used to quantify the amount of representation bias occurring in various experimental situations. Through this, the relationships between field design parameters and representation bias are explored, and the importance of plot dimension and spacing, as well as treatment to plot allocation, emphasized.

Development and validation of a model describing the curd induction of winter cauliflower

Summary A simulation model was proposed to predict changes in apex development during the curd induction phase of winter cauliflower (Brassica olerácea var. botrytis L.). The model included a continuous asymmetric function for temperature based on a gamma distribution using only two parameters. The model was fitted to data for the two winter cauliflower selections ‘March’ and ‘December/January’. The temperature function implied little apex expansion below 4 and 8°C for ‘March’ and ‘December/January’ respectively but the upper limit of 17°C was the same for both selections. The modal value of 9.4°C for ‘March’ was lower than that for ‘December/January’ at 11.7°C. The model accurately predicted progress through curd induction on independent data sets for each selection.

Assessment of suitable designs for field experiments involving airborne diseases

The suitability was assessed of various designs for field experiments investigating plant diseases caused by airborne pathogens that can be subject to interplot interference. Use of a model to describe such interference showed that the treatments with the most dissimilar effects on controlling the disease should be allocated to experimental plots furthest apart in each block, in order to minimize the interplot interference within a block. When using large square plots, rectangular blocks were more efficient than square blocks in minimizing treatment-comparison biases due to interference between neighbours. For rectangular blocks with the square plots side by side, less biased treatment comparisons were obtained from designs with complete blocks than from designs with incomplete blocks, especially when larger numbers of treatments were included in the experiment. However, when interplot variance is taken into account, incomplete blocks may give better treatment comparisons. Similarly, unbalanced designs composed only of incomplete blocks that yield less biased treatment comparisons may be better than balanced incomplete block designs when interplot variance is low. For high levels of variation, balanced incomplete block designs may be more appropriate, as increasing the precision of the treatment comparisons becomes more important than reducing the bias.

Building simple predictors for Narcissus timing and yield

Summary Data from three experiments with field-grown narcissus, starting in 1995, 1996 and 1997 and grown for two years, were used to develop simple descriptive relationships predicting crop timing, flower number and bulb yield. Treatments were designed to alter the temperatures to which the bulbs were exposed, and consisted of twelve combinations of two pre-planting storage temperatures (pre-cooling and no pre-cooling), two planting dates (early and late) and three straw mulch treatments (no mulch, early mulch and late mulch). Treatments were applied only in the first year of each experiment, but crops were sampled regularly over both years to provide data for model development. Non-linear models were fitted separately to pre-cooled and non-cooled crops to predict the time from planting to emergence in year one. A linear function of temperature above a base of 1.5°C described progress from emergence to flowering in both years although the rates for year one and year two crops differed. The yield of bulbs in year one was highly correlated with rainfall accumulated between planting and leaf senescence. The yield of bulbs in year two was determined by rainfall from planting in year one, rainfall from emergence in year two and by day-degrees >0°C accumulated between flowering and leaf senescence in year two. The number of flowers in year two was correlated with bulb yield in year one and therefore to the rainfall from planting to senescence in year one.

The effects of soil-applied aluminium sulphate, soil pH and soil potassium on pepper spot development in two winter white cabbage cultivars

SummaryTwo winter white cabbage cultivars, one tolerant (Little Rock) and the other susceptible to pepper spot development during storage (Langedijk 3 Decema) were grown in 1978 and 1979 in an experiment in which soil pH was reduced by treatment with Al2(SO4)3 and the K status increased by the application of KCl. Neither treatment affected yield. Lowering pH greatly increased pepper spot only in the sensitive cultivar, whereas increasing the level of K fertilizer increased plant K concentrations and also slightly decreased pepper spot in both cultivars. Although the major element concentrations differed between cultivars the treatment effects on them were small and unrelated to symptom development; pH had a major influence on minor element composition in both cultivars. The degree to which pepper spot developed was positively related to the Ni concentration. A greater Mn concentration in the tolerant cultivar apparently suppressed any Ni-induced pepper spot and a regression model combining the Mn and Ni c...