R. M. Crassweller

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.

Machine Vision Inspection of ‘Golden Delicious’ Apples

A machine vision system was developed to form a basis for single-pass quality feature inspection and grading of ‘Golden Delicious’ apples. The inspection criteria were based on USDA standards for fresh market apples. Image analysis algorithms were developed to assess and quantify the quality features of color, shape, and russet. Over 300 ‘Golden Delicious’ apples were inspected by the machine vision system and the results were compared to a human inspector. The vision system was able to correctly classify 100% of the apples for color, 92.3% for shape, and 82.5% for russetting.

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

AUTOMATED CYCLED SPRINKLER IRRIGATION SYSTEM FOR FROST PROTECTION OF APPLE BUDS

An automated cycled overtree sprinkler irrigation system was implemented and tested in a 0.4 ha (1 acre) dwarf apple orchard to protect apple buds from cold temperatures. The system reduced water usage compared to a more conventional approach of continuous sprinkling. The control scheme was based on a system that monitored the environmental parameters (air temperature, wind speed, relative humidity) and bud temperatures, calculated the on and off times, and cycled the valve. The system was tested during three frost events in the spring of 1997. The control system successfully kept the bud temperatures above the critical level during two of three frost events. During one event the sprinkled orchard temperatures dropped below the critical temperature for a short duration but were warmer than the unsprinkled orchard temperatures. The average reduction in water during the three frost events tested was about 72% as compared to continuous water application using the same system.

Automation of an Intermittent Overhead Irrigation Frost Protection System for an Apple Orchard

An automated sprinkling frost protection system was developed and tested to reduce the environmental damage caused by excess irrigation. A computer algorithm made the initial “turn-on” decision, cycled the irrigation, and turned off the system when the frost event ended. The sprinkling turn-on decision is based on bud stage of development, air temperature, wind speed, relative humidity, and rate of temperature fall. Sprinkler on-off cycles were used to adjust for a recommended sprinkler application rate determined by an energy balance model. The automated system was tested on an apple orchard during one spring and two fall frost events in 1992 and two spring frost events in 1993. The system successfully kept the apple flower bud temperatures above the critical bud temperature during two of the four frost events, while the bud temperatures dropped below the critical values for short durations on the other two events. The system has the potential to save water as indicated by a water use reduction of 75% during one mild frost event compared with the conventional approach of continuous sprinkling.

Impact of Producer Risk Preferences on Selection of Fresh-Market Apple Training Systems

Two important choices for apple growers are which cultivar to grow and which training system to use. Stochastic dominance analysis was used in an economic evaluation of a 10-year study in Pennsylvania (USA) comparing three cultivars (‘Crimson Gala’, ‘Ginger Gold’, and ‘Fuji’) grown on four training systems (vertical axe, slender spindle, 4-wire low trellis, and offset V-axe). Stochastic dominance accounts for grower risk attitude in such decisions. Because of consistently high yields and prices, ‘Fuji’ is the only cultivar that ranks highly across all risk attitude categories. For growers willing to accept more risk for higher reward, offset V-axe and vertical axe are preferred training systems. Trellis systems are preferred by growers seeking to minimize risk.

Root and mycorrhizal fungal foraging responses to fruit removal in apple trees

Background and aimsRoot and mycorrhizal fungal foraging in nutrient-rich patches is an energy-intensive process, and shifts in carbon (C) availability may affect foraging strategies. We hypothesize that when trees are C limited, they will prioritize root and mycorrhizal hyphal growth in nutrient-rich soil patches.MethodsApple (Malus domestica Borkh.) trees with fruit were compared to trees with fruit removed to investigate the effect of reproductive effort and associated shifts in belowground C availability on root and arbuscular mycorrhizal (AM) fungal growth in unfertilized soil and localized nitrogen (N)-rich patches (containing inorganic or organic nitrogen).ResultsAcross nutrient treatments, fruit removal enhanced root production compared to fruiting trees. In fruiting trees, about four times more roots proliferated in the inorganic-N patch than in unfertilized soil or the organic-N patch. However, in trees with fruit removal, root proliferation was similar among nutrient treatments. Arbuscular mycorrhizal extramatrical-hyphal biomass was not affected by fruit removal but was greater in the organic-N patch than the inorganic-N patch or unfertilized soil. Fruit removal and N addition had modest effects on AM fungal colonization of apple roots and no effect on non-mycorrhizal fungal colonization.ConclusionsRoot and AM foraging for nutrients should be considered in the context of C availability. Apple trees may manipulate root foraging more than AM fungal foraging when C belowground is constrained.