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R. Provvidenti and C.L. Niblett

An Australian strain of passionfruit woodiness potyvirus (PWV-K) infected peas and caused a light to moderate mosaic consisting of chlorotic spots, veinal chlorosis, and some plant stunting. Resistance to PWV-K was found in pea cultivars and plant introductions (PI) known to be resistant to bean yellow mosaic virus (BYMV). In cross and backcross populations involving the resistant cultivar Bonneville (United States) and PI 140295 (Iran) with the susceptible cultivar Ranger, a single recessive gene was responsible for the high level of resistance to PWV-K. From crosses involving PI 391630 (China), which is resistant to BYMV but susceptible to PWV-K, and the cultivar Bonneville (resistant to both viruses), it was evident that different genetic factors conferred resistance to these two potyviruses. The symbol pwv is tentatively assigned to this newly recognized pea resistance gene. Three other Australian strains of PWV did not infect peas.

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Jody A. Goodrich

This research tested the hypothesis that 60Co ionizing irradiation degrades polysomes to monosomes, a process that reduces growth of Pisum sativum seedlings. Dry and imbibed seeds and 5-day-old seedlings were exposed to 1.8, 3.6, 7.2, 14.4, or 28.8 krad of 60Co irradiation. Immediately after irradiation treatments, dry and imbibed seeds were planted, and later seedlings were harvested and analyzed. Five 1-cm root-tip samples from 5-day-old seedlings were crushed and layered onto 15% to 60% sucrose gradients and centrifuged for 55 min. The samples were processed through an ISCO ultraviolet chart maker. The monosome and polysome weights were read and analyzed. The monosome content was greater in the irradiated 5-day-old seedlings than in seedlings from dry and imbibed seeds. The growth of 5-day-old irradiated seedlings and seedlings from imbibed seeds was less than that of seedlings from dry seeds. The reduced growth of the irradiated seedlings suggests damage to the polysomes. When protein synthesis in plant cells is altered, perhaps through RNA decoding mechanisms, growth may be partially or completely arrested. Using sensitive plants to establish the injurious effects of ionizing irradiation on living organisms can educate and alert society to the detrimental effects of overexposure to irradiation such as that caused by nuclear accidents.

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Erik S. Runkle and Royal D. Heins

For many plants, light quality has a pronounced effect on plant morphology; light with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio promotes stem elongation and a high R: FR, or blue light (B, 400 to 500 nm), suppresses it. In addition, FR light is required for rapid flowering in some species, particularly for long-day plants. Our objective was to quantify how flexible spectral filters, which selectively reduce FR, B, or R, influence plant height and flowering of the quantitative long-day plants Pisum sativum L. `Utrillo' and Viola ×wittrockiana Gams. `Crystal Bowl Yellow'. Plants were grown at 20 °C with reduced FR, B, or R environments or with a neutral density control (C) filter. Calculated phytochrome photoequilebria were 0.78, 0.73, 0.71, or 0.46 for the altered FR, B, C, or R environments, respectively. All filter treatments transmitted a similar photosynthetic photon flux. Sixteen-hour photoperiods were created with natural daylight supplemented with high-pressure sodium lamps positioned above filters. Viola grown under the FR filter never reached 100% flowering within 8 weeks, and visible bud appearance was delayed by at least 17 days compared to all other filters. The R and B filters enhanced peduncle length by at least 25% compared to the C or FR filters. In Pisum, average internode length was 2.2, 2.9, 3.4, and 3.7 cm under the FR, C, B, and R filters, respectively, all statistically different. Fresh and dry shoot weights were similar under the C and FR filters but were at least 35% greater under the B filter and 35% lower under the R filter.

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Rebecca J. McGee and James R. Baggett

In crosses between stringless and stringy podded pea cultivars, all plants of the F1 and backcross to the stringy parent had stringy pods. F2 ratios varied widely among crosses, and populations always had more stringy plants than expected, based on a single locus. The ratio of nonsegregating (stringy): segregating F3 families derived from stringy F2 plants fit a single-gene hypothesis in half of the crosses. Backcrosses of F1 to the stringless parent fit the expected 1:1 ratio when the pollen parent was stringless, but the reciprocal backcrosses showed a deficiency of stringless plants, suggesting that poor competitive ability of pollen bearing the stringless factor was the reason for deficiencies of stringless plants. It is concluded that stringlessness is controlled by a single recessive gene for which the designation sin-2 is proposed. A reduction in pod size, plant height, and number of wrinkled seed segregates was associated with stringlessness.

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I.L. Goldman and E.T. Gritton

In pea (Pisum sativum L.) the af gene replaces leaflets with tendrils, and the tac gene restores small leaflets to the terminal portion of the tendrils of afaf plants. Normal (AfAf-TacTac), afila (afaf-TacTac), and afila-tendrilled acacia (afaf-tactac) near-isogenic lines in three genetic backgrounds were evaluated for 2 years in two locations to determine allocation of foliage area and weight of foliage components throughout the growing season. The percentage of total leaf area and weight due to stipule, tendril, leaflet, and tac leaflet were measured three times during the growing season in each environment. Highly significant foliage-type effects were detected for the percentage of leaf area and weight due to stipule and tendril at each sampling date. The pea leaf canopy exhibits large fluctuations in area and weight component allocation throughout the growing season. At 28 days after planting, stipules comprised 34%, 76%, and 53% of the total leaf area, and tendrils comprised 6%, 24%, and 13% of the total leaf area in normal, afila, and afila-tendrilled acacia types, respectively. At harvest, stipules composed 43%, 60%, and 53% of the total leaf area and tendrils composed 15%, 40%, and 22% of the total leaf area in normal, afila, and afila-tendrilled acacia types, respectively. Results from this study demonstrate that significant seasonal variation in allocations of foliage area and weight components exists among these three foliage types.

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James R. Baggett and R.O. Hampton

The inheritance of tolerance to infection by bean leaf roll luteovirus (BLRV) in Pisum sativum L. was studied in the cross of cv. Parlay (sensitive to BLRV infection) × cv. Oregon Sugarpod II (BLRV tolerant). The parents, reciprocal F1, back-crosses, F2, and 234 random F3 families were screened in 1986 and 1987 in the field at Twin Falls, Idaho, under natural BLRV inoculation by aphids. Overall disease index scores for the F1, F2, and F3 were about intermediate between indices of the parents, with the F1 usually slightly higher than midparent values. Backcross disease indices were intermediate between the F1 and the respective parent involved. Distribution of individual F3 family indices was continuous and semi-normal. BLRV-sensitivity ranges within parents and selected cultivars, as well as segregating populations showed continuous variation and differed between the 2 years, suggesting that expression of a major gene was significantly influenced by natural variation in BLRV inoculation pressure and timing. An apparent “additive gene action” was probably an artifact of nonuniform timing and levels of infection within plant populations. Chi-square analyses of segregating populations indicated that a major recessive gene, called lrv, conferred BLR disease tolerance.

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J.M. Amurrio, A.M. de Ron, and M. Santalla

Twenty sugar pea (Pisum sativum L.) landraces common to northwestern Spain (Pontevedra), and potentially of interest as parental material, were evaluated at two locations and for 2 years to study the diversity among them for plant and pod physical quality traits. The main objective was to identify landraces that could be included in breeding programs. Highly significant differences among landraces were found for most of the pod traits, such as length, width, length/width index, fresh weight, and flowering date. Genotype–environment interactions were demonstrated for only three traits of the 10 investigated. High values for correlation coefficients were mostly found for pod traits, but highly significant ones (i.e., P ≤ 0.01) were found for traits other than for pods. Most of the landraces were variable for qualitative and quantitative traits. PSM-0070, PSM-0113, and PSM-0116 were superior for earliness and pod physical quality, but were heterogenous. PSM-0064, PSM-0066, PSM-0117, and PSM-0118 lacked pod parchment.

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Mark E. Lewis and Earl T. Gritton

The effectiveness of one cycle (C) per year of phenotypic recurrent selection was evaluated for improving tolerance of peas (Pisum sativum L.) to aphanomyces root rot (Aphanomyces euteiches Drech.). Each cycle included field-screening a population of F2 lines (summer), diallel intermating among lines selected from the field (fall greenhouse), and one generation of selfing F1 plants (spring greenhouse) to produce F2 lines for the next cycle. The schedule is repeated for each cycle. A blocks-within-replicates design was employed in the field screening of C1 and C2 to improve within-block homogeneity. Selection intensities were 12.4%, 11.1%, and 10.6% for C0, C1, and C2, respectively. Using the performance of a tolerant control line, Mn 108, as a basis of comparison, the realized gain in dry seed yield and survival was 32% and 68% from C0 to C1 and 22% and 115% from C1 to C2, respectively.

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Floyd V. Pumphrey and Robert E. Ramig

Regression analysis was used to establish the effect of maximum daily temperatures on fresh pea (Pisum sativum L.) yield during the reproductive stage of growth. Maximum daily temperatures below 25.6C had little influence on pea yield. Temperatures above 25.6C depressed yield; this adverse effect increased exponentially as maximum daily temperature increased linearly. Predicted decrease in fresh pea yield ranged from 16 kg/ha per heat degree day above 27C to 67 kg/ha per heat degree day above 35C.

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Kevin E. McPhee, Abebe Tullu, John M. Kraft, and Fred J. Muehlbauer

Plant breeders must be aware of sources of resistance to pathogens that affect their crops. Fusarium wilt caused by Fusarium oxysporum Schl. f. sp. pisi Snyd. & Hans. is a fungal disease that affects peas and is important worldwide. Resistance to the different races of the pathogen has been identified in adapted germplasm and from specific accessions in the United States World Collection of peas (Pisum sativum L.). The goal of this study was to evaluate the resistance to fusarium wilt race 2 in the Pisum core collection. Of the 452 accessions screened, 62 (14%) were resistant. The resistant accessions included accessions from P.s. ssp. elatius that were collected from 24 different countries. The wide distribution of resistance around the world precludes the identification of any single country or region as a source of resistance. Of the 62 accessions resistant to race 2, 39 are also resistant to race 1 based on data obtained from GRIN. One of the wild progenitors, PI 344012, possessed resistance to races 1 and 2.