James W. Travis

Rootstock effects on gene expression patterns in apple tree scions.

Like many fruit trees, apple trees (Malus pumila) do not reproduce true-to-type from seed. Desirable cultivars are clonally propagated by grafting onto rootstocks that can alter the characteristics of the scion. For example, the M.7 EMLA rootstock is semi-dwarfing and reduces the susceptibility of the scion to Erwiniaamylovora, the causal agent of fire blight disease. In contrast, the M.9 T337 rootstock is dwarfing and does not alter fire blight susceptibility of the scion. This study represents a comprehensive comparison of gene expression patterns in scions of the ‘Gala’ apple cultivar grafted to either M.7 EMLA or M.9 T337. Expression was determined by cDNA-AFLP coupled with silver staining of the gels. Scions grafted to the M.9 T337 rootstock showed higher expression of a number of photosynthesis-related, transcription/translation-related, and cell division-related genes, while scions grafted to the M.7 EMLA rootstock showed increased stress-related gene expression. The observed differences in gene expression showed a remarkable correlation with physiological differences between the two graft combinations. The roles that the differentially expressed genes might play in tree stature, stress tolerance, photosynthetic activity, fire blight resistance, and other differences conferred by the two rootstocks are discussed.

Diversity and Biogeography of Sooty Blotch and Flyspeck Fungi on Apple in the Eastern and Midwestern United States

Sooty blotch and flyspeck (SBFS) fungi on apple fruit were sampled from nine orchards in four midwestern U.S. states during 2000 and 30 orchards in 10 eastern U.S. states during 2005 in order to estimate taxonomic diversity and discern patterns of geographic distribution. Forty apple fruit per orchard were arbitrarily sampled and colonies of each mycelial phenotype were counted on each apple. Representative colonies were isolated, cultures were purified, and DNA was extracted. For representative isolates, the internal transcribed spacer (ITS) and large subunit (LSU) regions of ribosomal DNA were amplified and sequenced. In total, 60 SBFS putative species were identified based on ITS sequences and morphological characteristics; 30 of these were discovered in the 2005 survey. Modified Kochs postulates were fulfilled for all 60 species in an Iowa orchard; colonies resulting from inoculation of apple fruit were matched to the original isolates on the basis of mycelial type and ITS sequence. Parsimony analysis for LSU sequences from both surveys revealed that 58 putative SBFS species were members of the Dothideomycetes, 52 were members of the Capnodiales, and 36 were members of the Mycosphaerellaceae. The number of SBFS species per orchard varied from 2 to 15. Number of SBFS species and values of the Margalef and Shannon indexes were significantly (P < 0.05) lower in 21 orchards that had received conventional fungicide sprays during the fruit maturation period than in 14 unsprayed orchards. Several SBFS species, including Schizothyrium pomi, Peltaster fructicola, and Pseudocercosporella sp. RH1, were nearly ubiquitous, whereas other species, such as Stomiopeltis sp. RS5.2, Phialophora sessilis, and Geastrumia polystigmatis, were found only within restricted geographic regions. The results document that the SBFS complex is far more taxonomically diverse than previously recognized and provide strong evidence that SBFS species differ in geographic distribution. To achieve more efficient management of SBFS, it may be necessary to understand the environmental biology of key SBFS species in each geographic region.

Rootstock-regulated gene expression patterns in apple tree scions

Apple trees (Malus x domestica) do not reproduce true-to-type from seed. Therefore, desirable cultivars are clonally propagated by grafting vegetative material onto rootstocks. Although cloned cultivars are genetically identical, rootstocks influence horticulturally important cultivar traits, including tree size, disease resistance, and abiotic stress tolerance. Here, ‘Gala’ scions were grafted to seven different rootstocks that produce a range of tree sizes and grown in a greenhouse. Global gene expression patterns in the scions were compared using a DNA microarray representing 55,230 apple transcripts. Each rootstock triggered a distinct, reproducible scion gene expression pattern. Two thousand nine hundred thirty-four scion transcripts were differentially regulated, by a factor of two or greater, by one or more rootstocks. Transcripts from genes predicted to be involved in responses to stress and biotic and abiotic stimuli were disproportionately represented among the rootstock-regulated transcripts. Microarray data analysis based on tree size identified 116 transcripts whose expression levels were correlated with tree size. The correlation of transcript level with tree size was tested for 14 of these transcripts using quantitative polymerase chain reaction in a population of orchard-grown ‘Mutsu’ cultivar trees grafted onto rootstocks from a breeding population of multiple crosses. Of those tested, transcripts encoding predicted sorbitol dehydrogenase, homeobox-leucine zipper, and hevein-like proteins were confirmed as being expressed at higher levels in larger trees, while a transcript predicted to encode an extensin-like protein was confirmed as being expressed at higher levels in smaller trees. This study illustrates the utility of using rootstock-regulated phenotypes to identify genes potentially associated with horticulturally important traits.

A working description of the Penn State Apple Orchard Consultant, an expert system

Agricultural production has evolved into a complex business. It requires the accumulation and integration of knowledge and information from many diverse sources, including marketing; horticulture; insect, mite, disease, and weed management; accounting; and tax laws. Emerging sustainable practices require even more information (to substitute for purchased inputs) for implementation. Farm managers seldom have at their disposal all information available in a usable form when major management decisions must be made. Increasingly, modern growers must become experts in the acquisition of information for decision making in order to remain competitive. However, because integrating and interpreting information from many sources may be beyond the means of individual growers, they use the expertise of agricultural specialists. Unfortunately, the assistance of these specialists is becoming relatively scarce even as the complexity of agriculture is increasing. To alleviate this problem, current information must be structured and organized into an accessible system for growers and agricultural specialists. Because no organized structure is available for information storage and retrieval, technical information is often lost or unavailable to potential users. The use of electronic

Use of Gibberellic Acid for Management of Bunch Rot on Chardonnay and Vignoles Grape

Harvest bunch rot of wine grape, caused primarily by Botrytis cinerea, is a perennial problem limiting the productivity of eastern vineyards, especially on cultivars with compact clusters. The aim of the present study was to evaluate the effectiveness of gibberellic acid (GA) sprays at reducing the compactness of Chardonnay and Vignoles clusters and minimizing bunch rot. Applications of GA reduced the number of berries per centimeter and the incidence and severity of bunch rots in Vignoles and, to a lesser extent, in Chardonnay over three consecutive years; however, the magnitude of GA effects often depended on the timing and rate of application. Bloom GA applications were more effective (P < 0.001) at reducing compactness and bunch rots than prebloom applications. Significantly, negative effects of GA applications on yield were negligible based on data from 4 years of trials on single vines and 2 years of data on 24-vine plots of Vignoles, provided the rates did not exceed 25 ppm. Regression analysis showed that berries per centimeter accounted for between 89 and 94% of variation in the incidence of Botrytis rot on Vignoles. On Chardonnay, compactness accounted for 53% of the variation in incidence, and the estimated compactness level at which no bunch rot would occur was 4.40 ± 1.05 (mean ± standard error) berries per centimeter. The relationship between cluster compactness and spray coverage of berries was also investigated in two separate experiments. Spray coverage of individual berries decreased linearly as cluster compactness increased within the range tested (3 to 18 berries per centimeter). Cluster compactness accounted for two-thirds of the variation in individual berry coverage, and coverage was reduced by 40 to 50% for clusters with about 18 berries per centimeter. These results strongly support the use of GA in integrated management of bunch rot on Vignoles and Chardonnay in eastern U.S. vineyards.