Variation for Seedling Root Architecture in the Core Collection of Pea Germplasm

bauer, 1996). Many pea diseases common in production areas affect root growth and function, thereby limiting Root growth is an important component of plant growth but has productivity (Kraft and Pfleger, 2001, p. 67). Tolerance received little attention by plant breeders because of difficulties associto many root diseases has been attributed to rapid root ated with root observation. Improved root architecture and production growth and production of large root mass; however, are likely to improve pea (Pisum sativum L.) production because they are often grown on marginal land and suffer from increased improved root growth parameters have not always been disease pressure and poor fertility. The objective of this study was to correlated with increased productivity (Kraft and Boge, quantify the phenotypic variation in seedling root production among 2001). However, analysis of seedling root characters has Pisum germplasm and to classify the root architecture observed. Seed been shown to relate well to root production under field of 330 accessions from the core collection of Pisum germplasm were conditions (Kraft and Boge, 2001; Veitenheimer and germinated and grown under artificial conditions for 14 d and their Gritton, 1984). Prolific root growth is not only expected root characters analyzed. Root systems were scanned and digitized to provide an advantage to the plant in the presence of by the WinRHIZO program. Data collected included taproot length, pathogens, but also under conditions where herbicide shoot length, and root and shoot dry weight. Data generated by Windamage may occur (Ali-Kahn and Snoad, 1977). Many RHIZO included total root length, surface area, average root diameherbicides applied to the pea crop have potential to ter, and root volume. Taproot length ranged from 181 to 433 mm, while root and shoot dry weight ranged from 6 to 57 mg and 13 to damage plant growth when taken up by roots. Rapid 104 mg, respectively. Total root length ranged from 54 to 399 cm, growth and proliferation of lateral roots would provide root surface area ranged from 9 to 75 cm2, and root volume ranged plants an opportunity to avoid severe damage and possifrom 0.11 to 1.12 cm3. Seed weight was significantly correlated with bly death. all root characters with the exception of taproot length. Shoot and Improvement in root architecture has been the result root dry weight were positively correlated with total root length, of indirect selection for disease tolerance or overall proaverage root diameter, and root volume. PI 261631, an accession from ductivity. Studies of root growth and function have been Spain, produced the greatest total root length, had a root:shoot weight conducted on pea over the last 75 yr; however, reports ratio of 0.79, and the largest root volume (1.12 cm3). Plant breeders are few and intermittent in the literature (Jean, 1928; will be able to use the wide variation for root characters in their Kraft and Boge, 2001; Veitenheimer and Gritton, 1984; crossing and selection programs to modify root traits during cultivar development. Zobel, 1974). Jean (1928) demonstrated that heritable variation exists in pea and that root growth was directly related to the phenotype of the shoot. Veitenheimer and Gritton (1984) studied 42 freezing and canning pea P breeding has largely ignored root production genotypes and found significant variability in the root because of difficulty in observing root growth under and shoot characters evaluated; however, this variability natural conditions. Relatively few and sporadic reports was not related to previously expressed tolerance to of variation for root characters and their genetic control root rot caused by Aphanomyces euteiches Drechs. f. are available despite their importance to plant growth. sp. pisi W.F. Pfender & D.J. Hagedorn. Roots are responsible for sessile plant growth and funcRoot characters are controlled by approximately onetion to absorb nutrients and water from the soil. Roots third of the plant genome (Zobel, 1975) and should not of leguminous crops such as pea also function as a host be ignored by plant breeders. An understanding of the to Rhizobium leguminosarum through symbiotic associrelationship between various root traits and plant proations. The Rhizobium form nodules in root hairs and ductivity is necessary before improvements can be fix gaseous nitrogen (N2) into ammonia (NH3) a form achieved. A comprehensive summary of the root traits the plant can use. The fertility benefit from N2 fixation which vary among pea germplasm and the degree of is an added benefit from the use of pea and other lethis variation is lacking in the literature. The objectives gumes in crop rotations throughout the world. of this study were (i) to quantify measurable root traits Pea is traditionally produced in marginal areas and among a diverse collection of Pisum accessions and (ii) receives little attention from producers compared with to classify the architectural variation in pea seedling other crops such as wheat, Triticum aestivum L. (Muehlroot systems. USDA-ARS and Crop and Soil Sciences Dep., Washington State Univ., Pullman, WA 99164-6434. Received 14 Sept. 2004. *CorreMATERIALS AND METHODS sponding author ([email protected]). Seed Source and Growth Conditions Published in Crop Sci. 45:1758–1763 (2005). Seed of 330 pea accessions from the core collection of Pisum Plant Genetic Resources germplasm was harvested from field plots in 1997 and stored doi:10.2135/cropsci2004.0544 at 4 C and low humidity before analysis (McPhee and Muehl© Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA bauer, 2001). The accessions were chosen at random from a 1758 Published online August 1, 2005