In order to evaluate and compare adaptability to dry sites, plant water relations and leaf gas exchange were compared in response to water stress among six birch species: monarch birch (Betula maximowicziana), river birch (B. nigra), paper birch (B. papyrifera), European birch (B. pendula), `Whitespire' Japanese birch (B. platyphylla var. japonica `Whitespire'), and gray birch (B. pendula). After 28 days without irrigation, Japanese birch maintained significantly higher stomatal conductance (gs) and net photosynthesis (Pn) than did any of the other species, despite having one of the lowest mid-day water potentials. Evaluation of tissue water relations, using pressure-volume methodology, showed no evidence of osmotic adjustment for any of these species in response to water stress. However, there was substantial variation among species in the water potential at the turgor loss point; varying from a high of -1.34 MPa for river birch to a low of -1.78 MPa for Japanese birch. Rates of Pn and gs under mild stress (mean predawn leaf water potential of -0.61 MPa) were negatively correlated with leaf osmotic potential at full turgor and the leaf water potential at the turgor loss point.
Thomas G. Ranney, R.E. Bir, and W.A. Skroch
J. C. Neal and W. A. Skroch
Thirteen species of woody ornamentals were treated over-the-top with glyphosate in a 6 × 6, rate by time factorial experiment. The influence of application timing on glyphosate phytotoxicity was significant for all species. The times of maximum tolerance and injury were species dependent. Species were organized into 4 response groups based on the effects of application time. Group 1 species, including ajuga (Ajuga reptans L.), azalea (Rhododendron obtusum Planch. ‘Coral Bells’), and a variegated liriope (Liriope muscari L.H. Bailey), were injured on all application dates. Species in groups 2, 3, and 4 exhibited tolerance to fall applications of glyphosate. Group 2, including wax leaf privet (Ligustrum japonicum Thunb.), sustained maximal injury from spring applications. Group 3 species, including Compacta holly (Ilex crenata Thunb. ‘Compacta’), were injured most by summer applications of glyphosate. However, Blue Rug juniper (Juniperus horizontalis Moench ‘Wiltonii’), a representative of group 4, was tolerant of glyphosate applications, sustaining only temporary tip chlorosis from spring and early summer treatments. First season evaluations were not sufficient to describe the ultimate effects of glyphosate on plant quality. Visual and objective evaluations in the 2nd growth season also were necessary. Chemical name used: N-(phosphonomethyl) glycine (glyphosate).
J.M. Shribbs and W.A. Skroch
Two-year-old ‘Smoothee Golden Delicious’ apples (Malus domestica Borkh.) on seedling rootstock were planted in Spring 1981. Twelve different ground cover systems were then established. After one growing season, trees in mulch, bare ground, red sorrel (Rumex acetosella L.), and nimblewill (Mulenbergia schreberii J. F. Gmel.) treatments had greater shoot length than trees in legume, tall broadleaf, Kentucky bluegrass (Poa pratensis L.), orchardgrass (Dactylis glomerata L.), and ‘KY31’ tall fescue (Festuca arundinacea L.) treatments. In the 4th year, the trunk diameter of trees in straw mulch plots were greater than all other treatments. Tree growth in bare ground and cultivation treatments was not different over the 4 years and was as great or greater than in treatments with living ground covers. Trees in tall broadleaf, Kentucky bluegrass, orchardgrass, and tall fescue treatments were smaller than in all other treatments. Nimblewill, a native species to North Carolina mountains, has potential for replacing Kentucky bluegrass, orchardgrass, and tall fescue in orchard soil management systems.
J.M. Shribbs and W.A. Skroch
Two-year-old ‘Smoothee Golden Delicious’ apples (Malus domestica Borkh.) on seedling rootstock were planted into cultivated soil in Spring 1981, and 12 ground cover systems were then established. Apple leaves, twigs from pruning cuts, soil samples, and ground cover clippings were analyzed for nutrient content in 1983 and 1984. Leaf N content had the highest positive correlation with tree growth. Leaf P and K contents were negatively correlated with leaf N and tree growth. Twig N, P, K, Mg, Ca, and Zn contents were positively correlated with leaf N content and tree growth. Soil nitrate content was positively correlated with tree growth and leaf N content. Results implicate N competition as a major factor of interaction between apple trees and grass and broadleaf ground covers.
W. A. Skroch, T. J. Monaco, T. R. Konsler, and P. B. Shoemaker
Azide as NaN3 or KN3 impregnated on clay granules gave excellent control of yellow nutsedge (Cypetus esculentus L.) compared to methyl isothiocyanate combined with chlorinated C3 hydrocarbons (Vorlex) or a non-hand weeded control. Nematode control was obtained with all treatments. Significant yield responses from the use of azide were obtained with all crops.
E. A. Estes, W. A. Skroch, T. R. Konsler, P. B. Shoemaker, and K. A. Sorensen
Staked tomatoes (Lycopersicon esculentum Mill) grown in 8 soil management systems are compared for differences in marketable yields, gross revenues, treatment costs, and net economic values. Maximum marketable yields were obtained using a fumigant and straw mulch combinatory practice, but the highest net economic value (gross revenues less treatment costs) was realized by a fumigant and herbicide ground management practice. These data suggest that the use of mulch materials and/or herbicides increased yields and net returns over standard cultivation practices.
H.M. Ariyarathne, D.P. Coyne, G. Jung, P.W. Skroch, A.K. Vidaver, J.R. Steadman, P.N. Miklas, and M.J. Bassett
Diseases of beans (Phaseolus vulgaris L.) are primary constraints affecting bean production. Information on tagging and mapping of genes for disease resistance is expected to be useful to breeders. The objectives of this study were to develop a random amplified polymorphic DNA (RAPD) marker linkage map using 78 F9 recombinant inbred (RI) lines derived from a Middle-American common bean cross Great Northern Belneb RR-1 [resistant to common bacterial blight (CBB) and halo blight (HB)] × black A 55 [dominant I gene resistance to bean common mosaic potyvirus] and to map genes or QTL (quantitative trait loci) for resistance to CBB, HB, BCMV (bean common mosaic virus), and BCMNV (bean common mosaic necrosis virus) diseases. The RI lines were evaluated for resistance to leaf and pod reactions to Xanthomonas campestris pv. phaseoli (Xcp) (Smith Dye) strain EK-11, leaf reactions to two Pseudomonas syringae pv. phaseolicola (Psp) (Burkholder) Young et al. (1978) strains HB16 and 83-Sc2A, and BCMV strain US-5 and BCMNV strain NL-3. The linkage map spanned 755 cM, including 90 markers consisting of 87 RAPD markers, one sequence characterized amplified region (SCAR), the I gene, and a gene for hypersensitive resistance to HB 83-Sc2A. These were grouped into 11 linkage groups (LG) corresponding to the 11 linkage groups in the common bean integrated genetic map. A major gene and QTL for leaf resistance to HB were mapped for the first time. Three QTL for leaf reactions to HB16 were found on linkage groups 3, 5, and 10. Four regions on linkage groups 2, 4, 5, and 9, were significantly associated with leaf reactions to HB strain 83-Sc2A. The gene controlling the hypersensitive reaction to HB 83-Sc2A mapped to the same region as the QTL on LG 4. The I locus for resistance to BCMV and BCMNV was mapped to LG 2 at about 1.4 cM from RAPD marker A10.1750. Five and four markers were significantly associated with QTL for resistance to CBB in leaves and pods, respectively, with four of them associated with resistance in both plant organs. A marker locus was discovered on LG 10, W10.550, which could account for 44% and 41% of the phenotypic variation for CBB resistance in leaves and pods, respectively. QTL for resistance in pod to CBB, leaf resistance to HB, and the I gene were linked on LG 2.