Bush Blue Lake Research Articles

Changes in flavonoids secreted by Phaseolus vulgaris roots in the presence of salt and the plant growth-promoting rhizobacterium Chryseobacterium balustinum

Root exudates affect the concentration of nutrients in the plant rhizosphere and indirectly enhance microbial activity. Flavonoids are polyphenolic compounds that play an important role as signal molecules in the early stages of the symbiosis between legumes and rhizobia. Flavonoids from root exudates of Phaseolus vulgaris cv. Bush Blue Lake obtained under control conditions, salt stress (50mM), and/or the presence of the plant growth-promoting rhizobacterium (PGPR) Chryseobacterium balustinum Aur9 were analyzed by HPLC coupled to ESI-MS/MS. Six flavonoids were identified in the root exudates of P. vulgaris cv. BBL: naringenin, isoliquiritigenin, quercetin umbelliferone, 7′,4-dihydroxyflavone, and hesperetin. The latter three flavonoids have not previously been reported in bean root exudates. The presence of C. balustinum, but not salt stress, modified the pattern of flavonoids exuded by the bean roots. The capacity of flavonoids from root exudates to induce the expression of the nod genes and the production of lipochitooligosaccharides (LCOs) was investigated in two bean-nodulating rhizobia, Rhizobium tropici CIAT899 and Rhizobium etli ISP42. The R. etli ISP42 LCOs profile changed when it was induced by the exudates collected in the presence of the PGPR with and without salt. In the case of R. tropici CIAT899, changes in the LCOs profile were detected when the bacterium was induced with the different bean root exudates in comparison with the LCOs synthesized upon induction with apigenin.

EFEITO DO ORGASOL NA CULTURA DE FEIJÃO-DE-VAGEM (Phaseolus vulgaris L.) NA PRESENÇA E NA AUSÊNCIA DE ADUBAÇÃO QUÍMICA

The Orgasol, an organic compound of animal origin, was tested on seeds and on snap crop ( Phaseolus vulgaris L. cv. Bush Blue Lake), with and without chemical fertilizer (NPK) in two planting dates. The orgasol-s with three applied doses (0, 1 and 2 ml/l of water on a first date and 0, 3 and 6 ml/l, on a second date) had no influence on seed germination and pods production on this crop.

Integrated Management of Angular Leaf Spot (Phaeoisariopsis griseola (Sacc.) Ferr.) on Snap Beans in Ontario

Angular leaf spot (ALS) caused by the fungus Phaeoisariopsis griseola (Sacc.) Ferr. was first observed and confirmed on snap beans growing in three commercial fields in southern Ontario during the 2000 growing season. The potential impact of this disease on the bean industry in Ontario is not known but this disease is severe in many other regions. The objective of this study was to develop a disease management strategy for ALS in Ontario by investigating the survival of P. griseola in Ontario, and assessing the influence of bean varieties and fungicides on disease development. P. griseola survived at least one winter on crop debris in Ontario and survived better on the soil surface in comparison to burial in soil at depths of 5 or 25 cm. Fifteen snap bean varieties were compared for susceptibility to ALS in a growth room, and nine varieties were compared in a naturally-infested field from 2001-2003. Most varieties reacted similarly to P. griseola in both environments. For example, the varieties Carlo, Storm, and Bush Blue Lake 47 were least susceptible whereas Gold Rush was most susceptible in field and growth room experiments. Boscalid, pyraclostrobin, pyramethanil, vinclozolin, and thiophanate-methyl were tested for effectiveness in managing ALS under field conditions. Overall, pyraclostrobin was most effective. Results indicate that an effective disease management strategy for ALS in snap bean in Ontario should include burying infested plant debris through deep plowing, crop rotation for two years, growing the least susceptible varieties, and applying a registered effective fungicide. Accepted for publication 13 October 2005. Published 29 November 2005.

Genetic Control of O3 Sensitivity in a Cross Between Two Cultivars of Snap Bean

Identification of genetic control of ozone (O3) sensitivity is desirable for selection of plant cultivars which are indicators of O3 stress. A cross was made between two cultivars of snap bean (Phaseolus vulgaris L.), `Oregon 91' (P1) and `Wade Bush' (P2), an O3-sensitive and O3-insensitive cultivar, respectively. Ten genetic populations (generations), `Oregon 91' (P1), `Wade Bush' (P2), F1, F2, backcrosses to both parents, and all reciprocal crosses, were field planted in each of two summers and evaluated for injury to O3. Ozone responses for the reciprocal crosses were not significantly different for any generation, so injury ratings from the reciprocal crosses were combined for each generation to provide six populations (P1, P2, F1, F2, BC1, and BC2) for analysis. When components of genetic variation were estimated from the six generations, additive genetic variance was the most important component in the total genetic variance available, although dominance variance was also a significant component. There was an inconsistency in the magnitude and the direction of the factors contributing to the dominance effects and also a large environmental component making up the phenotypic variance. Estimates of broad-sense heritability and narrow-sense heritability were 60% and 44%, respectively. Results suggest that O3-sensitive and O3-insensitive selections could be screened and evaluated in an ambient O3 environment. Several generations will be necessary, however, to develop `Bush Blue Lake' type selections that vary only in sensitivity to O3.

Mechanisms of ethylenediurea (EDU) induced ozone protection: Reexamination of free radical scavenger systems in snap bean exposed to O 3

Ethylenediurea (EDU), N- [2-(2-oxo-1-imidazolidinyl) ethyl]-N′-phenylurea is known to prevent ozone (O 3) damage to leaf tissues. However, the mechanisms of protection are unclear. We tested the hypothesis that EDU protects against O 3 damage by scavenging hydroxyl free radicals (OH). An in vitro study involving the use of high-performance liquid chromatography equipped with an electrochemical detector (HPLC-EC) showed that EDU does not serve as an antioxidant to remove OH free radicals. Effects of O 3 and EDU (soil drench) on leaf antioxidant scavenger systems (AOSS) were also studied. The first fully expanded trifoliate leaves of O 3-sensitive snap bean ( Phaseolus vulgaris cv. Bush Blue Lake 290) was examined. Measurements were made before and after a single O 3 exposure (0.30 μl 1 −1 O 3 for 3 h). Pretreatment with EDU 48 h before exposure protected against O 3-induced necrosis and chlorosis. EDU pretreatments did not alter superoxide dismutase (SOD), guaiacol-peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR) activities. However, O 3-fumigated plants (no EDU) showed elevated SOD activity with decreased GR activity. EDU-treated plants exposed to O 3 stress showed no measurable loss of GR activity. These tissues maintained high levels of total glutathione [i.e. reduced glutathione (GSH) + oxidized glutathione (GSSG)] contents, and had higher GSH/GSSG ratios than the controls at the end of 3 h exposure to O 3. These data suggest that EDU protection against O 3 damage in plants do not necessarily involve the direct stimulation or induction of antioxidative enzyme defense mechanisms. Instead, protection may result from a more general retention of chlorophyll and maintenance of GR and GSH levels during O 3 exposure.

Characterization of Ice Nucleation and Propagation in Bean (Phaseolus vulgaris cv. Bush Blue Lake) using Infrared Video Thermography

Frost-sensitive plant species have a limited ability to tolerate ice formation in their tissues. Most plants can supercool below 0°C and avoid ice formation. Discrepancies exist about the role of intrinsic and extrinsic ice-nucleating agents in initiating ice formation in plants. Previous research has demonstrated the ability of infrared video thermography to directly observe and record the freezing process in plants (Wisniewski et al., 1997. Plant Physiol. 113:4378–4397). In the present study, the ability of droplets of a suspension of the ice-nucleating-active (Ice+) bacterium, Pseudomonas syringae, and droplets of deionized water, to induce ice formation in bean plants was compared. The activity of these agents were also compared to intrinsic ice formation in dry plants. Results indicated that the presence of the Ice+ bacteria in droplets ranging from 0.5–4.0 μL always induced freezing at a warmer temperature than droplets of deionized water alone (no bacteria) or intrinsic nucleators in dry plants. When droplets of Ice+ bacteria were allowed to dry, they were no longer effective but were active again upon rewetting. Droplets of water would often supercool below temperatures at which ice formation was initiated by intrinsic agents. When a silicon grease barrier was placed between the droplets of Ice+ bacteria and the leaf surface, the bacteria were no longer capable of inducing ice formation in the plant, despite the droplets being frozen on the plant surface. This indicates that ice crystals must penetrate the cuticle in order to induce freezing of the plant.

Metal Levels in Garden Vegetables Raised on Biosolids Amended Soil

Biosolids compost was applied annually over a four year period to a Christiana silt loam soil at the rates of 73 and 146 Mg/ha. Two study areas were established at the site with slightly different experimental designs. Composite soil samples were analyzed for pH and levels of Pb, Zn, Cu, Ni and Cd. Vegetables grown on these plots included bush Blue Lake green beans (Phaseolus vulgaris, L.), crookneck summer squash (Cucurbita pepo, L.), zucchini squash (Cucurbita pepo, L.) Golden Bantam sweet corn (Zea mays, L.), black-seeded Simpson lettuce (Lactuca sativa, L.), Bloomsdale long-standing spinach (Spinacea oleracea, L.) and dwarf blue curled Yates kale (Brassica fimbriata, L.). Plant tissue samples were analyzed for uptake of Pb, Zn, Cu, Ni and Cd. The soil pH was found to increase with increasing application rate. Control plots which received lime had significantly higher pH than unlimed control plots. Statisticially significant differences in soil metal levels between treated and control plots were observ...

382 PRECISION SEEDING STUDIES ON SNAP BEANS

Field studies were. conducted in 1992 and 1993 to evaluate vacuum planters with respect to precision placement of seeds and to separately study plant spacing and emergence uniformity on stand establishment and yield. All studies were. performed with Bush Blue Lake 47. In 1992, a cooperative study was conducted with the Experiment Station and ten growers in Upstate New York representing four makes of commercial planters. No planter was able to precision seed, and seedling emergence revealed a large tendency to clump plant, with less errors made in the form of misses or skips. In 1993, tractor planting speed was studied as a variable from 3.4 to 12.3 KPH (2.1 to 7.6 MPH) on spacing uniformity and yield. The average number of seedlings per meter of row was similar for all treatments, however, the variation in spacing between plants generally increased as planter speed increased. In research plots, in-rowspacing and emergence uniformity were studied. Plant population was held constant and three in-row spacings were. developed (1 plant 5 cm apart, 2 plants 10 cm apart or 3 plants 15 cm apart). There were. no differences in yield in this study. Daily emergence was recorded and seedlings were grouped into three categories based on their time to emergence (early, medium or late). Yield was more than twice as much from early than late emerging seedlings, while the medium group was intermediate with respect to yield.

475 PB 373 INHERITANCE OF A TWISTED POD CONDITION IN PHASEOLUS VULGARIS L.

An abnormal pod condition, in which bean pods are twisted, sometimes as much as 360°, was discovered in a selection of OSU 5256, a Bush Lake breeding line. The amount of twisting of affected pods and the number of affected pods/plant are both variable. F2 progenies from crosses between twisted pod line 5256-1 and two normal bush Blue Lake cultivars segregate 3 normal:1 twisted, showing that the twisted mutant is controlled by a single recessive gene.

GLK-8903 Reduces Membrane Phospholipid Peroxidation and Alleviates Chilling Injury in Phaseolus vulgaris L.

Twenty-day-old `Bush Blue Lake 47' common bean plants grown in a growth chamber at 25 days/22C night and a 12-hour photoperiod regime were foliar sprayed with 0.5% GLK-8903 including 0.05% Tween-20. After 24 hours of treatment, plants were chilled in a cold room (4C day/night, 12 hours of light). After 3 days of chilling, leaves of untreated controls were injured, as visually characterized by leaf wilting, whereas leaves of the GLK-8903-treated plants still retained turgor. During chilling, the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) decreased. GLK-8903 treatment had no effect on SOD and POD activities; however, the CAT activity was reduced significantly after GLK-8903 treatment either at 25 or at 4C. During chilling, the content of malondialdehyde, a decomposition product of phospholipid peroxidation, increased in treated plants and untreated controls, with increased content significantly lower in the former compared with the latter. The GLK-8903 per se and total lipid extracted from GLK-8903-treated plants were able to reduce the linoleic acid oxidation in vitro. The mechanism by which GLK-8903 alleviates chilling injury in bean plants is discussed.

Retaining the Benefits of Matriconditioning by Controlled Drying of Snap Bean Seeds

The effects of various drying conditions on seed quality and performance of matriconditioned `Bush Blue Lake 47' snap bean (Phaseolus vulgaris L.) seeds were studied. An exponential model based on the Page equation provided a good fit (R2 = 0.9) to changes in moisture content during drying. Drying matriconditioned seeds with high initial moisture content (47.2%) for 5 to 6 hours at 35C, 30% to 35% relative humidity, and 0.7 to 1.4 m·s-1 air velocity (v) retained, and in some cases augmented, the benefits derived from conditioning. Matriconditioning greatly reduced electrolyte leakage (34.3 vs. 94.7 μS·cm-1·g-1 for nontreated seeds); drying to 15% moisture content at 0.7 or 1.4 m·s-1 v moderately increased the leakage rate (59.1 to 60.9 vs. 34.3 μS·cm-1·g-1), while drying at 0.02 m·s-1 v (ambient) increased the rate to that of nontreated seeds. The leakage rate remained low (43.6 to 50.8 μS·cm-1·g-1) in matriconditioned seeds dried to 22% moisture content at all air velocities. In growth-chamber studies, rapidly drying matriconditioned seeds to 15% moisture content at 1.4 m·s-1 v improved the emergence percentage over that of nontreated seeds, increased the shoot fresh and dry weight over that of nontreated and nondried matriconditioned seeds, and increased the shoot fresh weight over that of seeds dried at 0.02 or 0.7 m·s-1 v. Drying matriconditioned seeds to 15% moisture content at 0.7 m·s-1 v improved plant fresh weight over that produced by nontreated seeds. Rapid drying to 22% moisture content at 1.4 or 0.7 m·s-1 v improved only shoot fresh weight over that of nontreated seeds. In a 1992 field planting, percent emergence of matriconditioned seeds dried at 0.7 or 1.4 m·s-1 v was similar to that of nondried matriconditioned seeds and higher than that of nontreated seeds. No significant differences were noted in plant yield among the treatments.

Flooding Affects Snap Bean Yield and Genotypic Variation in Leaf Gas Exchange and Root Growth Response

Greenhouse experiments were conducted in 1987 and 1988 to evaluate the effect of timing of a 4-day flooding stress on growth and yield of snap bean (Phaseolus vulgaris L. cv. Bush Blue Lake 274, BBL). Plant survival was reduced when flooding was imposed at postflowering growth stages, but most plants survived when flooded before flowering or when reproductive development was prevented by deflowering. Early yields of surviving plants were very low in all flooded treatments, regardless of timing, in both years. Total yield response to timing of flooding was linear in 1987, with lowest yields when flooding was imposed at later growth stages. The trend was not linear in 1988, but in both years the latest flooding treatment (36 days after planting) had few surviving plants and no measurable pod yield. Additional greenhouse experiments revealed that leaf conductance of BBL and another bean cultivar, Luna (LN), declined within the first day of flooding. This decline was concomitant with one in leaf water potential and photosynthesis (Pn) in BBL, but decline of these responses occurred 1 to 2 days later for LN. After 4 days of flooding, Pn fell to near 0 for BBL, and to 15% of the prestress value for LN. Pn of both cultivars had recovered to 18.5 μmol·m-2·s-1 10 days after termination of flooding. LN had a larger adventitious root biomass, higher percentage of adventitious roots, and a consistently lower leaf: root ratio than BBL during recovery.

The Antiozonant Ethylenediurea Does Not Act via Superoxide Dismutase Induction in Bean

It has been proposed that the mode of action of ethylenediurea, a very effective antiozonant, is via an increase in the antioxidant enzyme superoxide dismutase (EH Lee, JH Bennett [1982] Plant Physiol 69: 1444-1449). Data presented here refute that hypothesis. No ethylenediurea-associated increases in Cu/Zn-superoxide dismutase or Mn-superoxide dismutase activity, nor in steady-state Cu/Zn-superoxide dismutase protein levels, were found in soluble extracts of bean (Phaseolus vulgaris L. cv Bush Blue Lake 290) leaves. However, the cytosolic Cu/Zn-superoxide dismutase increased as a result of ozone fumigation and subsequent injury. Also noted was a developmentally related difference between chloroplastic and cytosolic Cu/Zn-superoxide dismutase, the latter declining during maturation of the leaf.

Vitamin-Humic-Algal Root Biostimulant Increases Yield of Green Bean

Over the past decade there has been a not-able increase of research on the use of nat-urally derived or organic materials inagriculture (Poincelot, 1986; Russo and Ber-lyn, 1990). Some of these are biostimulants,i.e., nonnutritional products that may reducefertilizer use and increase yield and resis-tance to water and temperature stresses.Among the materials that stimulate plantgrowth in relatively small amounts (Aitkenet al., 1964; Berlyn and Russo, 1990; Kin-nersley et al., 1989; Senn, 1987; Senn andKingman, 1973) are humic acids, marine al-gae, polymers of lactic acid, B vitamins, andascorbic acid. Under certain conditions,biostimulants work well (Russo and Berlyn,1990) and suggest possible uses in horticul-ture.We tested “Roots” (Lisa Products Corp.,New Haven, Conn.), a proprietary mixtureof humic acids, marine algae extracts, thia-mine, and ascorbic acid. The objective ofthis study was to assess the effectiveness ofthis organic biostimulant (OB) on pod pro-duction of green beans (Phaseolus vulgarisL.).Seeds of beans cv. Bush Blue Lake 274(Agway Inc., Syracuse, N.Y.) were sownand germinated in trays filled with vermi-culite. In test A, the first set of 120 seedlingswas transplanted, one seedling per pot, to2.8-liter pots that contained a 1 potting soil(Agway) : 1 vermiculite (v/v) mix. The sta-tistical design was a completely randomizedfactorial (Statview II, Abacus Concepts,

Responses of Closely Related Bush Blue Lake Snap Bean Cultivars to Increasing Concentrations of Ozone

Eight Bush Blue Lake type snap bean (Phaseolus vulgaris L.) lines and cultivars with similar genetic backgrounds were container-grown to green-pod maturity in open-top field chambers while being exposed to chronic doses of 03 for 7 hours·day-1 for 42 consecutive days. Treatments included charcoal-filtered air, nonfltered air, and 0.02, 0.04, or 0.08 ppm O3 added to nonfiltered air. Visible injury was estimated during the 2nd week of exposure and compared to the green pod yield data. The presence of four yield response groups, as determined via regression analysis, indicated the presence of variation for 03 sensitivity in the germplasm pool, but all eight lines were O3 - sensitive with yield losses at 03 levels exceeding a 7-hour daily mean of 0.085 ppm. Foliar injury may be a good indicator of general yield loss; however, estimates of visible injury lack the precision necessary to distinguish subtle differences among a collection of O3-sensitive snap bean lines.

EDU and ozone protection: Foliar glycerolipids and steryl lipids in snapbean exposed to O3

Effects of the antiozonant EDU, N‐[2‐(2‐oxo‐1‐imidazolidinyl) ethyl]‐N'‐phenylurea, on the content and composition of foliar lipids in snapbean (Phaseolus vulgaris L. cv. Bush Blue Lake 290) before and after a single, acute ozone (O3) exposure were assessed. Pretreatment with EDU conferred protection against O3‐induced necrosis and losses of glycerolipids and chlorophyll. Systemic treatment of snapbean plants with EDU did not significantly alter membrane lipids in the first trifoliate leaf. Leaves of untreated controls had lost ca 50% of both galacto‐ (GL) and phospholipids (PL) by the end of a 3 h exposure to 0.4 μl l−1 O3. A decline in the ratio of mono‐ to di‐galactosyldiacylglycerol (MGDG/DGDG) was associated with the loss of GL, and a decline in the ratio of linoleic to linolenic acid (18:2/18:3) was associated with the loss of PL in untreated controls. EDU‐treated plants showed no significant loss of foliar GL and PL. The MGDG/DGDG ratio declined only slightly, and the 18:2/18:3 ratio in PL increased during O3 exposure of EDU‐treated seedlings. The level of total membrane sterols, including free sterols (FS), acylated steryl glycosides (ASG) and steryl glycosides (SG), did not change during O3 exposure of either treated or untreated plants. However, in the controls the proportions of ASG and SG increased at the expense of FS, and the ratio of stigmasterol/sitolsterol increased in FS and SG. In EDU‐treated plants, a relatively small increase in SG was offset by a decrease in FS, and there was no change in the stigmasterol/sitosterol ratio in ASG, SG or FS. The results indicate that EDU may confer tolerance to O3 through induction of enzyme systems involved in the elimination of activated oxygen species and free radicals.

Generation mean analysis of inheritance of insensitivity to ozone injury in two crosses of beans(Phaseolus vulgarisL.)

The inheritance of bean (Phaseolus vulgaris L.) foliar insensitivity to ozone (03) was studied using generation mean analyses (GMA) as the genetic design. The following GMAs were evaluated: ‘Bush Blue Lake (BBL) 290’ x PI 304833, and ‘BBL 254’ x PI 300657. The six populations (P,, P2, F,, F2, F, x P,, and F, x P2) comprising a GMA from each cross were planted in 15 cm plastic pots as a randomized complete block design with three replications. When unifoliate leaves were about two-third expanded and maximally sensitive to 03 they were fumigated with non-filtered ambient (NF) + 0.06 ppm 03 concentration in open top field-fumigation chambers. Data on percent leaf 03 injury were recorded. The mean rated values of the incidence of O, injury in the F, generation were lower than the mid-parent values in both crosses, suggesting that insensitivity may be dominant over sensitivity. A genetic model with additive-dominance effects was fitted to generation means in ‘BBL 290’ x PI 304833, and ‘BBL 254’ x PI 300657 and...

Enhanced Mn accumulation by snapbean cultivars under FE stress

Abstract Iron deficiency in dicots is accompanied by an increased potential for Fe uptake and translocation. The mechanisms responsible for these changes in metabolism (Fe‐stress response) provide for the adaptation of Fe‐efficient genotypes to conditions which limit the availability of Fe. Previous studies indicated that when Fe‐stress response is initiated, the uptake of Mn, as well as Fe, is enhanced in Fe efficient species such as sunflower. The present study was conducted to determine the relationship between Fe‐stress response and Mn uptake in snapbean (Phaseolus vulgaris L., cvs. Bush Blue Lake 290, Bush Blue Lake 274). The plants were grown in complete nutrient solutions containing 0.02 to 0.52 mg L‐1 Mn, at acid or alkaline pH. Iron stress was induced with 0.22 mg l‐1 Fe(EDDHA) (molar ratio 1:1 or 1:2), high P (14.3 mg L‐1) and excess CaCO3. Bush Blue Lake 290 ('BBL 290') was more sensitive than Bush Blue Lake 274 ('BBL 274') to Mn toxicity in acid (pH 5.2) nutrient solutions with adequate Fe. Un...

Cold tolerance in beans (Phaseolus spp.) as analyzed by their exotherms

Cold tolerance of common bean (Phaseolus vulgaris L.), runner bean (P. coccineus L.) and several bean lines was evaluated under artificial conditions. Seedlings were exposed to −6°C gradually, then to −12°C rapidly in the growth chamber with copper-constantan thermocouples attached to various parts of the plant. Seedling freezing curves with exotherms were then analyzed. Three basic parameters were measured: time required for exotherm to appear, temperature of the appearance of the exotherm and temperature rise caused by the exotherm. Exotherm appearance in beans was related to freezing injury and death of the seedlings. Exotherms of the common bean variety Bush Blue Lake 92 seedling recorded at the stem, primary leaf base, tip and petiole and true leaf appeared at the same time, however their shape was different. Exotherms of stem appeared at higher temperature than those of primary leaves. Their shapes always followed the same pattern. Beans with cold tolerance were found to produce exotherms later than susceptible ones. Exposing 3 weeks old bean seedlings to 12°C delayed the time of exotherm appearance in the cold susceptible cultivar Bush Blue Lake 92. Some plants survived 2 hours exposure to −6°C in the growth chamber.

Modified Bean Pod Assay to Detect Strains of Pseudomonas syringae pv. syringae That Cause Bacterial Brown Spot of Snap Bean

Consistent results were obtained with a procedure that involves placing a smear of bacterial cells on the pod surface and inserting an insect-mounting pin through the cells and laterally underneath the epidermis of greenhouse-grown snap bean pods (cultivar Bush Blue Lake 274). Since the procedure does not require calculated inoculum concentrations, it is useful in evaluating large numbers of strains (e.g. epiphyte collections) for their ability to cause BBS. Pod assays were more rapid and reliable than leaf assays of whole plants in distinguishing strains of P. v. pv. syringae capable of causing BBS