Edaphic Parameters Associated with Shore Juniper Decline

Fravel, D. R., Benson, D. M., and Bruck, R. I. 1983. Edaphic parameters associated with shore juniper decline. Phytopathology 73:204-207. In the absence of evidence of a biotic agent as the primary cause of decline parameters of the A+B horizon were better indicators of decline than those of shore juniper (Juniperus conferta), abiotic factors were examined to of the C horizon. Supportive evidence for the involvement of these determine their roles in contributing to decline. Six of 20 edaphic components was provided by tissue nutrient analysis from landscape components measured in 20 landscape plantings were significantly plantings and from greenhouse studies of nutrient deficiencies and water interrelated to decline index in a multivariate principal axis factor analysis. stress in which nitrogen deficiency and, in one case, both water excesses and These parameters were calcium, clay + silt content, magnesium, nitrate, deficiencies, induced symptoms resembling decline. phosphorus, and zinc. Where soil horizons could be distinguished, Additional key words: abiotic stress. Shore juniper, Juniperus conferta Parl., is a low-growing shrub SJD, investigations were undertaken to examine abiotic agents as that has increased in popularity as a landscape plant in North causes of or factors contributing to SJD. The sensitivity of shore Carolina during the past several years. The numbers of shore juniper to low dosages of ozone, alone and in combination with juniper specimens submitted to the North Carolina Plant Disease NO 2 and SO 2, has been reported elsewhere (4). The roles of certain and Insect Clinic also increased during this period. Many of these edaphic components in SJD are discussed in this article. plants showed symptoms of a previously undescribed decline. Symptoms of decline included chlorosis of the older needles that MATERIALS AND METHODS progresses to necrosis, beginning at the soil line and advancing up Edaphic components study. Twenty landscape plantings of shore the plant stem. Stunting, root necrosis, and small, tan foliar lesions juniper representing different severity levels of SJD were selected in were observed less frequently. Research was undertaken to Wake County, NC. Plantings had been in place a minimum of 3 yr. determine the etiology of shore juniper decline (SJD). At each site, 20 plants, approximately one plant per square meter, A root and crown rot, wilting, stunting, and death were reported were rated for SJD as follows: I = no symptoms, 2 = chlorosis on to be caused by either Phytophthora cinnamomi Rands, P. the basal third of the plant, 3 = chlorosis and some necrosis on the nicotianae Dast. var. nicotianae (Breda de Haan) Tucker, Pythium basal third, 4 = lower third of plant necrotic, 5 = lower third of irregulare Buisman, or P. sylvalicum Campbell & Hendrix (7). In plant necrotic and chlorosis of the middle third, 6 = basal third repeated, replicated greenhouse experiments, inoculation of 1-yrnecrotic and some necrosis of the middle third, 7 = basal two-thirds old plants with P. cinnamomi-infested oat grains produced necrotic, 8 = lower two-thirds necrotic and chlorosis of the top symptoms resembling those of decline after 6-8 wk (4,5). Plant size third, 9 = lower two-thirds of plant necrotic and some necrosis of indices and root and shoot fresh weights were also significantly the upper third, and 10 = plant dead. smaller in P. cinnamomi-inoculated plants than in those inoculated Approximately 500 cm' each of surface soil (A+B horizons) and with sterile oat grains or not inoculated. Because root necrosis is subsoil (C horizon) were collected at each site. Where soil was generally assotiated with P. cinnamomi infection but not with homogeneous to a depth of 30 cm, only one sample was taken. SJD, P. cinnamomi was not considered a primary cause of SJD. When the C horizon was encountered in the first 30 cm, A+B and C A binucleate, Rhizoctonialike fungus was consistently recovered horizons were collected separately. Depth of the A+B horizon was from surface-disinfested needles of shore juniper. Inoculations of recorded. Soil color was determined by the Munsell soil color book shore juniper with 13 of these isolates under conditions of several (Munsell Products, Baltimore, MD 21233). Color code letters were variations of relative humidity, host water potential, inoculum converted to numeric values as follows: 1 = 1 YR, 2 = 2.5 YR, 3 = 4 placement, wounding, and inoculum substrate failed to produce YR, 5 = 7.5 YR, and 6 = 10 YR. Thus, the higher numbers indicate decline symptoms (4). Inoculations with eight other fungi, as well as decreasing soil redness. Soil mottles were rated by the following naturally infested debris, also failed to induce decline symptoms scale: 0 = none, I = few, 2 = moderate, 3 = abundant, and 4 = (4). Populations of plant parasitic nematodes at decline sites were numerous. The proportion of sand and clay + silt was determined considered too low to be a probable contributing factor in SJD (4; by wet sieving 10 g of soil (oven dry weight, 60 C for 24 hr). Sand D. M. Benson, unpublished), retained by a sieve with a 53-jim opening was collected, oven-dried In the absence of a detectable biotic agent as the primary cause of 24 hr at 60 C, and weighed. The proportion of clay + silt was determined by subtraction. Acidity, pH, cation exchange capacity, The publication costs of this article were defrayed in part by page charge payment. This base saturation, percent organic matter, and weight per volume article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. § bulk s ity) were de term by t g ic DivonNot 1734 solely to indicate this fact. (bulk density) were determined by the Agronomic Division, North Carolina Department of Agriculture (NCDA). Exchangeable and ©1983 The American Phytopathological Society extractable anions and cations (calcium, copper, magnesium,