ASHS 2024 Conference

Increasing orchard planting density has helped improve grower profits and yields but establishment costs can be high. It is believed that by using bi-axis trees the number of trees required during planting can be reduced while possibly improving yields and fruit quality. To test this possibility, an orchard of four cultivars (‘Brookfield Gala’, ‘Aztec Fuji’, ‘Honeycrisp’, and ‘Ruby Mac’) was established and trained to either Tall Spindle (TS) or Bi-axis (BA) at 1m x 4m spacing. After the third year of growth, all TS trees and half of BA trees were summer hedged, resulting in three systems to compare: 1) TS hedged; 2) BA hedged; and 3) BA non-hedged. Measurements of trunk cross sectional area (TSCA), phenology, yield, and fruit quality were recorded for seven years to calculate cumulative values. At the end of the study, TSCA was larger on TS trees compared to hedged or non-hedged BA trees across cultivars. Biennial bearing was lower with ‘Brookfield Gala’ and ‘Aztec Fuji’ compared to ‘Honeycrisp’ and ‘Ruby Mac’ and trended lower on hedged or non-hedged BA trees than TS trees. The hedged or non-hedged BA trees had higher cumulative yields compared to TS trees across cultivars. Fruit size was reduced on hedged or non-hedged BA trees compared to TS trees, but all three systems had similar fruit color, firmness, and soluble solids on average. After seven years, there was no obvious benefit of using hedged or non-hedged BA systems to improve fruit quality, but higher yield from BA trees over TS trees when planted at the same density, regardless of hedging during the summer, was achieved. We calculated that BA trees could be planted at 15% lower planting density than TS trees to achieve the same yield.

In 1977 Avery published a review of apple leaf photosynthesis (Pn) rates to estimate maximum rates with current technologies and conditions. This presents a recent review of more than 90 published reports of apple photosynthesis from 1978-2022 evaluated the techniques and equipment used, the experimental parameters of CO2, temperature, light, and vapor pressure deficit. The goal of the review was to determine if techniques used reflected changes in global atmospheric [CO2], and if there was evidence of response of apple leaves to changing [CO2] with time. Avery in 1977 estimated mean apple Pn rate to be ca. 14 µgCO2m-2s-1 and a maximum rate of ca. 22 µgCO2m-2s-1. The current review suggests an estimated mean apple Pn rate to be ca. 15.6 µgCO2m-2s-1 , similar to Avery, but a maximum rate of ca. 31-35 µgCO2m-2s-1, higher than Avery. Since 1977, there has been an approximately 26% increase in global CO2. There was no correlation between experimental [CO2] or atmospheric [CO2] and reported Pn, and although reported Pn rates tended to increase with time, there was no significant correlation to time. Experimental[CO2] was reported in 58% of the reports but omitted in others. Experimental parameters of measurement temperature or vapor pressure deficit were commonly not reported.

Somatic mutations in apple commonly develop into viable bud sports for cultivation. When an apple bud sport has a desirable attribute such as improved color, size, shape, flavor, firmness, sweetness, or harvest timing, it has potential to be introduced as a new cultivar that growers utilize, and consumers enjoy. The genetic mutations and related mechanisms associated with early or delayed maturation (respectively resulting in early or late harvest date) in apple sports are not known despite their value to the industry. By acquiring knowledge about these genetic mutations and their respective molecular mechanisms, breeders can identify markers to conduct more informed crosses to select for early or late maturing apple lines. Apple lines with differing developmental rates resulting in differing ‘designed’ harvest windows would optimize the deployment of field laborers for the apple harvest and improve use of cultural practices to influence harvest time. Comparison of physiology-based markers of fruit developmental stages for apple sports with different maturation dates has been done, but, to the author’s knowledge, not on trees for which crop load has been appropriately adjusted to eliminate its effect on developmental rate. In this study, crop load was regulated on 6 different apple cultivars according to tree trunk cross-sectional area. The sports selected were the ‘Gala’ sport ‘Autumn Gala’ also known as ‘Harry Black’, the early maturing ‘Fuji’ sport ‘September Wonder Fuji’, and the early maturing ‘Cripps Pink’ (‘Pink Lady®’) sport ‘Maslin Cripps Pink’. These three sports were compared to their progenitor/standard harvest time cultivar. Apple fruits were measured on each of five trees per cultivar, and volumetric growth rate was analyzed. We found that in each comparison, fruit growth rate of the early variant was significantly greater early in fruit development, roughly coinciding with the expected conclusion of the cell division phase based on phenology. Consequently, a narrower window of genetic events responsible for the early or late harvest timing phenotype has been captured. Our work confines the search for genetic events responsible for the harvest date mutations to the early developmental stages for apple fruit. We propose that harvest date in these apple bud sports is physiologically predetermined from the very early stages of fruit development and very likely not a function of strictly ripening-related processes.

The apple U-Pick market in Ohio lacks diversity in varieties to meet consumer demand outside of those typically available at grocery stores. Apple growers want new cultivars that are suited for growth in the Midwest, ripen across the picking season, and intrigue customers with unique flavors, textures, and traits. These diverse and unique tasting apples exist, but it is difficult to market these apples without a comprehensive understanding of the traits and consumer desirability of these fruits. This project aims to identify and characterize sensory traits in 33 up-and-coming apple selections including commercial, in-development, and wild varieties with novel characteristics suited for local production. Apple selections were chosen in conjunction with apple specialists at The Ohio State University and local apple growers. Consumer perception and apple traits were evaluated through two sets of sensory experiments: consumer hedonic testing and descriptive analysis. Consumer testing was conducted in private sensory booths, where apple slices were provided in a randomized, blinded order to mitigate order effects. One hundred participants rated apples on their appearance, texture, flavor, and overall liking on a 9-pt hedonic liking scale (i.e., dislike extremely to like extremely). Descriptive analysis was conducted by 12 trained panelists who used references as anchors on a 10-pt scale to score important appearance, aroma, flavor, and texture fruit characteristics. Measured characteristics were decided in collaboration with the panel organizer, trained panelists, and included traits of particular interest to growers. The trained panelists rated 26 traits like red color, floral notes, sweetness, and crispness. Anchors were carefully selected to provide precise references along the scale, such as sucrose solutions of varying concentration to calibrate judgements of sweetness. To compare how different factors of the apple related to each other, correlation analyses were run on the datasets. Flavor liking had the strongest positive correlation with overall liking, followed by texture liking, while appearance liking showed a weaker positive correlation. Sweetness exhibited a slight positive correlation with overall liking, whereas sourness showed the opposite. Using mean separation tests, we identified 15 apple selections liked equivalently to Honeycrisp, a top commercial apple. Further phytochemical analysis will enable gaining insights on nutritional quality profile and its relation to consumer preference. Our goal is to provide information on novel apples that will enable apple growers to diversify their offerings, which will also benefit producers and consumers.

The Maryland Tree Architecture Project (MD-TAP) used classical plant breeding methods to create, identify, select and then patent grower-friendly apple trees. The project began in 1991 with the open pollination of 'McIntosh Wijcik' trees set in an isolated 'Gala' block. Elite seedlings resulting from that initial cross then served as male parents in an open-pollination of commercial cultivars well-adapted to the warm, wet, windy, Mid-Atlantic climate. Two scion-dwarfed, apple trees producing good quality fruit and demonstrating a reduced susceptibility to fire blight resulted from this effort. These two selections were patented as 'MD-TAP1' and 'MD-TAP2' in 2023. A replicated field trial was set in 2016 to compare these two scion-dwarfed selections, with their wild-type siblings also from this program. Trees were budded onto 'M.111,' a semi-dwarfing rootstock to assess their growth habit and tree size without the benefit of trellis support or sustained annual pruning. Trees were set at a 2.75 by 4.25 m (9 by 14 ft) spacing and are still manageable. Despite annual pruning, they are similar in height to trees in an adjacent tall-spindle planting budded onto dwarfing rootstocks. The University of Maryland concluded two Materials Transfer Agreements (MTAs) with other universities before the patents were allowed. After patenting, the University began contacting commercial nurseries in the Mid-Atlantic Region for future testing and licensing.

Rapid apple decline (RAD), a phenomenon that causes sudden decline and death of young apple trees in high-density orchards, is a pressing issue. This problem has been associated with abiotic (flood, drought, freeze) and biotic stressors (fungi, bacteria, and insects). Ambrosia beetles (AB) (Xylosandrus spp.) have been linked to stressed trees suffering from RAD. However, the direct association is still not clear. We evaluated the effects and interactions of rootstock (‘B. 9’, ‘M. 7’, and ‘G. 41’) and water stress (flood, drought, control) on physiological responses and AB colonization. Specifically, a greenhouse experiment was performed in spring 2023 on 14-month-old potted ‘MAIA1’ trees. Trees were subjected to water stress for 20 d. Water stress treatments consisted of a saturated pot-in-pot system for flood, water with-held for the duration of the experiment for drought, and irrigation based on soil moisture, maintaining the pots between 0.7 and 1 water fraction volume for control trees. The experiment had a randomized complete block design, was replicated 10 times, and had a factorial treatment structure. Measurements were made every 2 d for soil moisture, fluorometry, and spectrometry data, every 4 d for leaf gas exchange and midday water potential, at 7 and 14 d for ethanol volatiles, and at the termination of the experiment for AB colonization. Under control conditions, ‘G. 41’ trees had higher transpiration, stomatal conductance, and assimilation rates than ‘B. 9’ and ‘M.7’ trees. However, after 4 d of stress, ‘G. 41’ showed a more rapid decline in leaf gas exchange parameters relative to other rootstocks. Drought-stress trees from the three rootstocks declined 4 d faster than flood trees during the first 12 d. However, this decline occurs more abruptly in ‘G. 41’ and ‘M. 7’ trees. From 16 to 20 d, drought and flooded trees have a similar response. Under control conditions, all three rootstocks have similar quantum efficiency values. Conversely, under water stress, ‘G. 41’ and ‘M. 7’ declined faster than ‘B. 9’ trees, with a more severe response to drought for ‘G. 41’ and ‘M. 7’ trees. Chlorophyll index (Ci) showed lower values for flood and drought trees after 10 d for ‘G. 41’ and ‘M. 7’ trees. For ‘B. 9’, this was only true in drought trees. Flooded trees had AB tunnels three times longer than control, and drought trees were the only ones where AB larvae were observed, which was linked to higher ethanol levels.

Photosynthesis is well-known to not only occur in leaves but also other tissues like stems, sepals, and fruits. Fruit photosynthesis has been documented in cucumber, tomatoes, satsuma mandarins, prickly pear, wheat, and apple. Fruit photosynthesis occurs in these instances not only to contribute to carbon assimilation but to support other metabolic processes, the synthesis of metabolites, and seed development. Early fruit growth in apple is regulated by energy-intensive cell division that lasts for approximately five weeks before switching to a phase of predominantly cell expansion-driven growth. Thus, fruit photosynthesis during early fruit development in apple could function to fulfill the resource and energy requirements necessary for the growth and development of fruit tissues. To examine this potential contribution of photosynthesis to apple fruit metabolism, shade bags made of 30%, 65%, and 80% shade cloth were placed on fruitlets at 16 days after full bloom. The effects of fruit shading on fruit tissue plastid ultrastructure, metabolite composition and tissue transcriptomes were analyzed. Using transmission electron microscopy (TEM), we found that plastids in the peel and cortex overall resembled that of photosynthetically active plastids; they contained stromal and granal thylakoids similar to those found in leaves. Spatially, pith plastids displayed unique hypergranal features , with increased granal thylakoids and a significantly reduced presence of stromal thylakoids. When compared to the control, 80% shaded peel plastids contained more plastoglobuli, and 80% shaded pith plastids displayed prolamellar bodies, which are indicative of disassembly. Further, significantly lower chlorophyll a concentration was observed in shaded fruit. Metabolite analyses indicated that sorbitol was significantly greater in shaded fruit than in the control. Transcriptome analyses indicated substantial changes associated with carbohydrate metabolism in the fruit cortex and peel in response to fruit shading. Together, these analyses indicate a significant contribution of fruit photosynthesis to early fruit growth and development in apple.