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A method was developed to measure void areas and subsequent canopy development patterns in alfalfa plots and fields as affected by winter injury. The method utilizes aerial infrared photography, taken sequentially throughout the growing season, or year to year as well, followed by electronic measurements of the photographs. The method demonstrates that strong canopy recovery takes place throughout the growing season and a considerable amount of the damage is not permanent.

Optical density signatures were developed from infrared photographs of plots infected with late blight caused byPhytophthora infestans (Mont.) d By. Slight differences between optical density signatures of plots with different spray schedules preceded corresponding differences in infection levels that were not visually apparent on the date of photography but were visually apparent later. The technique of density signature development allowed consistent and quantitative differences to be recorded.

Methodology was developed utilizing remote sensing techniques to separate and quantitatively measure the various components of alfalfa (Medicago sativa L.) fields containing void areas as well as short grass and weeds. Infrared color film was exposed over mixed hay fields in the Carp and Vernon regions of eastern Ontario in the spring of 3 successive yr (1974–1976). Ground observations were made to ascertain field conditions to confirm the location and the interpretation of dense or sparse alfalfa, tall or short grass, weeds and void areas on the photographs. In 12 representative fields, the percentage of alfalfa, grass and void areas was determined for each year by image area measurements based on optical densities of the photographs. Analysis of soil and alfalfa root samples from these fields confirmed the absence of the root rot pathogen Phytophthora megasperma Drechs. or any other fungi pathogenic to alfalfa. Saprophytic species of Fusarium and Pythium were prevalent in each field. The genera of nematodes found in the samples were not considered harmful to alfalfa. Therefore, an estimated 14% loss of alfalfa was attributed to winter injury during the 3-yr period. The amount of grass increased by 28% and void areas decreased by 14% in these fields.

Optical densities from aerial infrared photographs of foliage of 11 (initially 50) field-grown oat cultivars could not be reliably used to distinguish cultivars with different protein content. Optical densities varied between replications and years; cultivars, however, maintained their relative high and low levels of protein over years and replications. Results from regression and canonical analysis largely failed to show a relationship between optical density and protein content.Key words: Oat protein, aerial photography

Vertical aerial photographs were taken over commercial pea (Pisum sativum L.) fields in the Picton-Wellington region, Ontario, in 1975 (a drought year) and in 1976 (a non-drought year) using Kodak Aerochrome Infrared film 2443. Optical separations into black and white images were necessary to assist in delineating healthy crop boundaries from severe root rot- and drought-affected areas (37.14%) as well as void areas (5.29%) from 1975 photographs of 12 selected fields. In these fields, excluding the void areas, an estimated yield loss of 22.7% was calculated by multiplying the percentage of the affected area by an average yield loss conversion factor of 0.61 derived from all available data from greenhouse- and field-grown plants of several commercial pea cultivars.

Aerial photographs of corn fields in southwestern Ontario were photographically enhanced and subsequently computer-analyzed to determine levels of corn aphid infestation. The flight line included 87 fields, 42 of which were infested to varying degrees. The levels of infestation varied from 35.6% to 67.1% determined from five representative fields.

Yield of white beans increased markedly (250, 1,090 and 1,545 kg/ha) when grown in field plots at soil temperatures of 11.6 (T1), 19.7 (T2), and 29.7 C (T3) (20-cm depth 0830 h). This represents a change in yield of 71.1 kg/ha per 1 C change in the seasonal temperature (T2) of the soil from 23 June to 21 August. The number of degree-day units for the soil (> 5 C) corresponding to these temperatures (20-cm depth) were 268, 602, and 1,004. A decrease in the Soil Moisture Index (SMI) from 0.69 to 0.10 and an increase from 0.69 to 1.00 lowered yield by 35% and 6%, respectively (T2), for the seasonal temperature. Loss in yield from plants infected with bacterial blight (Xanthomonas phaseoli E.F. Sm. Dows.) by spraying the organism onto leaves of 21-day-old seedlings was negligible. However, loss in yield from plants infected by injecting the organism into stems was 9.0, 43 and 52% for plants grown at cool (T1), seasonal (T2), and warm (T3) soil temperatures, respectively. Percent of pods infected by spraying was increased, whereas percent of pods infected by injection was decreased at the higher soil temperatures. In general under cool seasonal temperatures, protein content of the infected and noninfected beans decreased with higher moisture that coincided with only a small change in yield. The protein content, however, remained fairly constant under large yield increases resulting from higher soil tempratures. The data are interpreted in relation to spread of the disease in fields from seedborne infection and subsequent spread of the disease to adjacent healthy plants.

Aerial photography was used to record changes on spring emergence, growth and development of nine lines of fall-sown dormoats (Avenafatua L. × Avenu sativa L.). The effect of differential emergence was detectable throughout the growing season.

Based upon the reactions of seven pea varieties selected for their suitability as differential hosts, four distinct physiologic races of Ascochyta pisi Lib. were found among 80 isolates of the fungus obtained from diseased pea plants and infected seeds from six provinces in Canada. The geographic distribution of each of the races was as follows: I and II from the Prairie Provinces; III the Georgian Bay area and central Ontario, and IV the Ottawa Valley and to a lesser extent central and western Ontario, Quebec, and Nova Scotia.

A. pinodella and A. pinodes survived over a 12-month period in inoculated sterile soil maintained at a temperature range of −20 to 25 °C. Cultures isolated from soil from −20 °C to 15 °C were pathogenic; however, cultures isolated from soil at 5 and 10 °C were more virulent. A. pisi survived in soil at −20 and 5 °C for 12 months but only cultures isolated from −20 °C soil were pathogenic. The ability of soil cultures A. pinodella and A. pinodes to form chlamydospores is considered to a be a factor in their survival over this period of time and temperature range. No chlamydospores were formed in soil cultures of A. pisi. A. pinodella and A. pinodes were both antagonistic to A. pisi in sterile soil plates and A. pinodella was antagonistic to A. pinodes. Ascochyta spp., either A. pinodella or A. pinodes, were isolated from 18 of 46 soil samples collected from many areas in Canada. Soil cropped to corn contained fewer Ascochyta propagules than did soil cropped to beans, turnips, or peas; the latter soils contained the most propagules.

The effects of introducing new varieties and bacterial strains upon the epidemiology, ecology, and control of Xanthomonas phaseoli and X. phaseoli var. fuscans in registered bean seed crops in southwestern Ontario between 1961 and 1968 are described. A new phage type of X. phaseoli, Ib, is reported. Problems related to plant introductions and the detection of seed-borne pathogens are discussed.

Xanthomonas phaseoli var. fuscans (Burkh.) Starr & Burkh. in naturally infected bean seeds stored at −20 to 35 °C retained its viability, virulence, and physiological properties for 3 years. Agar cultures of the pathogen maintained at −20 to 20 °C also retained their pathogenicity and physiological characters throughout the test period but showed less virulence than the seed-borne isolates by the end of 33 months. The viability of agar cultures held at 25, 30, and 35 °C was lost after 24, 18, and 9 months of storage, respectively.The effects of 24 carbon sources on the growth of the pathogen have been determined. The production of a brown diffusible pigment by the organism was influenced by temperature, aeration, and the carbon source. Sugar alcohols did not support good growth or inhibit pigment formation. Most carbohydrates, which supported good or fair growth of the organism, seemed to inhibit pigment production or its expression.

Antibiotic XG has been studied for its possible application as a pea seed treatment in the control of Ascochyta leaf and pod spot. Fungistatic properties of Antibiotic XG against Ascochyta Pisi at various concentrations in relation to pH and temperature in vitro were studied. At antibiotic concentrations up to 1 p.p.m. no fungistatic effect was observed at pH values from 3.5 to 6.5, but, at concentrations above 1 p.p.m., complete inhibition of growth was found at all pH values tested. In the temperature range of 22 °C. to 30 °C. antibiotic concentrations of 1 p.p.m. had no effect on growth. Fungicidal activity to spores of A. Pisi has also been tested. A spore suspension of 10,000 spores per ml. required an exposure of 12 hr. with an antibiotic concentration of 100 p.p.m. for complete lethal dosage. The soaking of diseased pea seed samples in Antibiotic XG at a concentration of 25 p.p.m. for a period of 18 hr. effectively controls A. Pisi infection as determined by laboratory test and does not seriously impair germination. This treatment is compatible with Spergon applied after the seed has been air-dried. Storage of treated seed for a period of three months did not affect the degree of control but reduced the germinative capacity in laboratory plate tests.

Exposure of naturally infected and artificially inoculated seeds to radio-frequency (rf) electric waves of 59 to 64 Mc/sec was of varying effectiveness in eradicating internally borne fungi and bacteria. Diaporthe phaseolorum was eliminated from soybean seeds with little reduction in seed germination. Survival of Ascochyta pisi and A. pinodes (Mycosphaerella pinodes) in field pea seed was greatly reduced by similar treatment, but the fungi were not usually eradicated without appreciable reduction in germination. Germinability of pea seeds was unaffected by increasing the moisture content of the seed to 16% from 10.3%. The A. pinodes content of such seeds, however, was reduced by approximately 50%. Both seed and fungus were more susceptible to damage by rf treatment at the higher moisture level. Bean seed infected with Xanthomonas phaseoli var. fuscans and cabbage seed inoculated with X. campestris were killed by exposures which reduced but did not eradicate the bacteria. Colonies of both xanthomonads on nutrient agar media were destroyed by rf treatment.

Blight, caused by Mycosphaerella pinodes, is now epiphytotic and Ascochyta pinodes is the principal pathogen found in Canadian field pea seed. Ascochyta pisi, cause of leaf and pod spot of peas and formerly the principal seed-borne pathogen, is now seldom found. Reasons for this situation are discussed. Although infection by A. pinodes, from the seed to seedling stage, took place over a temperature range of 10 to 30 °C, the optimum range for infection was 15 to 18 °C. The symptoms produced at the different temperatures are described. Thiram 75, Orthocide 75, Panogen 15 and Spergon as seed treatments were effective in controlling the organism in sand, sandy loam and sterilized sandy loam. Thiram 75 and Orthocide 75 were equal in effectiveness and significantly better than Panogen 15 or Spergon.

A comparison of the Ulster, New Zealand, and Ottawa methods of seed examination for the presence of Polyspora lini Laff., the cause of stem-break and browning disease of flax, showed great variation in the percentage of infection obtained, depending upon the method used. The Ulster method, in which the seed is not treated before it is plated, does not differentiate deep-seated infection from superficial infection of the seed, but has proved satisfactory in actual practice with seed samples that are not contaminated seriously by saprophytic fungi. The New Zealand method, by which surface contamination is supposedly removed by washing the seed in running water, has not been found reliable. The Ottawa method, by which the seed is surface sterilized before it is plated, does not indicate the degree of superficial infection, but does give the percentage of deep-seated infection, and hence it indicates the suitability of the seed for planting purposes if the seed is treated with a fungicide. It is suggested that a centrifuge test combined with the Ottawa plating method would provide a better index of the health condition of flax seed as far as disease caused by. P. lini is concerned.

Isolates of Xanthomonas phaseoli var. fuscans (Burkh.) Starr & Burkh. obtained from naturally infected bean (Phaseolus vulgaris L.) seeds stored at 10 C for 2–4 months were more virulent, as indicated by a stunting effect on Sanilac bean plants, than isolates obtained from seeds stored for 7–24 months. Neither the rate of growth of the organism nor its ability to produce a brown diffusible pigment was correlated with virulence. Growth rate and pigment production of all isolates in nutrient broth were similar and reached a maximum after 36 and 48 h respectively. In a medium containing inorganic salts and yeast extract, the growth rate of the organism was relatively slow and pigment development depended upon amendments added to the medium. Tyrosine enhanced, while glucose retarded, pigment production, but neither affected the growth of the pathogen adversely. The formation and color of the pigment in the media were not affected by pH values ranging from 5.5 to 9.0. The presence of living cells was essential for the continued production of the pigment. The melanoid nature of the pigment was demonstrated.

Mycosphaerella pinodes Berk, and Blox. Vestgrn. and Ascochyta pinodella Jones were found to cause serious yield losses in the field. Although a higher percentage of seeds became infected with Ascochyta pisi Lib. than with either of the fungi referred to above, yield losses were considerably less, This finding is important in setting disease tolerances for various grades of seed since in the past arbitrary scales for these three organisms have been set without any knowledge of the relative importance of seed infection to field epidemiology. Only races III and IV of A. pisi caused significant losses in yield. Cycloheximide (100 p.p.m.) applied as a spray in the field significantly reduced seed infection by A. pisi but also reduced seed germination. Phygon 50W and griseofulvin 50W did not reduce germination but reduced seed infection considerably although not completely. Granted, preliminary results suggested that certain chemicals gave a selective control of the races of A. pisi, but this phenomenon could not be further demonstrated because of secondary infection in the field.

Diaporthe phaseolorum (Cke. & Ell.) Sacc., the causal agent of pod and stem blight of soybeans and generally regarded as a facultative parasite, has been found to be pathogenic during the seedling phase. The fungus caused severe losses of germinating seeds and young seedlings. In 1959 more than 30% of the soybean seed crop in southwestern Ontario was infected, and germination was severely reduced. D. phaseolorum was present in seed samples from this area in 11 of 13 years. Studies with a series of seed samples of varying levels of infection revealed that the fungus was still viable and pathogenic in the seed after storage for 2 years. However, during that time the levels of infection in most samples had decreased markedly whereas a concurrent increase in germinability indicated that infected seeds were killed during the germination phase. While several seed treatment fungicides were effective in increasing germination and emergence in heavily infected samples, none completely controlled the disease. At normal planting rates, yield was not affected by levels of seed infection up to 42% but the yield was significantly lower in a sample containing 73% infected seed. It is concluded that the disease may be important in the seed and seedling phases of host development.

Fuscous blight (Xanthomonas phaseoli var. fuscans), a new disease of field beans in Canada, was found to be present in a high proportion of bean seed samples from southwestern Ontario. Although symptoms of the disease are similar to those of common blight (Xanthomonas phaseoli), a greater intensity in color is apparent on infected seed and more hypertrophy, especially of nodal tissues, is caused by fuscous blight than by common blight. In epidemiological studies in the field, it was found that seed infection as low as 0.5% could cause a serious epiphytotic in the resulting crop. This points out the necessity of a zero tolerance for fuscous blight in valuable seed stocks. Furthermore the rapid phage plaque method can be used to determine zero tolerance. Garden varieties were generally more susceptible to the pathogen than field varieties. Great Northern showed the highest degree of resistance to the disease of all the varieties tested.An agar plating technique was developed whereby the organism can be isolated and identified in infected bean seed by the production of a brown diffusible pigment on nutrient agar. A bacteriophage spot test is also described which can also be used to identify the pathogen from infected bean seed. By means of phage typing, the relationship of X. phaseoli var. fuscans, X. phaseoli, and intermediate strains is shown.

Eight phage types of Xanthomonas phaseoli (E. F. Sm.) Dows. were identified by an experimental phage-typing system using four virulent phages and 310 isolates of this organism. The existence of phage subtypes was also demonstrated by the use of high-titer phage preparations. The phage subtypes could be located geographically. Correlation between strain virulence and phage subtype was demonstrated. Polyvirulent phage Pg 176 for X. phaseoli var. fuscans used in the typing system was partially characterized. The incidence and distribution of phages for strains of X. phaseoli and X. phaseoli var. fuscans in soil samples from southwestern Ontario from 1962 to 1965 were determined. The low ecological significance of soil-borne phage was demonstrated. Seventeen phages for X. phaseoli were isolated from 13 soil samples with the aid of enrichment, none without.

As part of a program for breeding horticultural varieties of peas resistant to Ascochyta pisi Lib., a study was made of the inheritance of resistance to a monospore isolate of the pathogen using a cross between the resistant pea strain, Ottawa A-100, and the susceptible variety, Thomas Laxton. The results indicate that resistance to the isolate used is due to duplicate dominant genes, either one of which will give resistance.

Ascochyta pinodella, cause of footrot, and Ascochyta pinodes, cause of blight, of peas were isolated from field soil by heating the soil to 100 C for 12–15 h followed by plating the soil on a medium containing rose bengal and chlortetracycline. A. pinodella was present in most soils where peas were growing and also in some soils where peas had not been grown for 1 to 5 years. Soil cultures of A. pinodella were weakly virulent but by host passage, re-isolated cultures produced typical symptoms of footrot on young plants. A. pinodes was isolated less frequently from soil; however, cultures were strongly virulent and inoculated plants showed typical disease symptoms in 5 days. Although infected seed has been considered to be the main source of inoculum, the frequent isolation of A. pinodes and A. pinodella from soil demands a re-appraisal of the epidemiology of this disease complex.

Specific immune serum against Ascochyta pisi was developed and three species-specific reactions were obtained by standard absorption techniques using extracts of both Ascochyta pinodella and Ascochyta pinodes. Ouchterlony tests showed a complex pattern of precipitation reactions in agar gel between the antigens from the three species and antisera developed in response to them and indicated distinct serological relationships among the three fungi. The pattern of reciprocal precipitin reactions indicates a closer serological relationship between A. pinodella and A. pinodes than between either of these two species and A. pisi. Two serologically similar antigenic components were present in the extracts from the three species.

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