Apples (Malus domestica, Borkh.) Phenology in Ethiopian Highlands: Plant Growth, Blooming, Fruit Development and Fruit Quality Perspectives

Fruit quality is the result of a complex interaction of management and environmental factors. By understanding the impact of environment, culture, harvesting, handling and storage on fruit quality, growers should be able to improve both average qualities in their crop as well as improving the proportion of fruit in the highest quality grade. Whilst management practices such as pruning, training, and crop regulation methods contributed widely for development of quality fruit. The relationships between apple rootstock-scion are important and provide a basis for selecting the best graft combination for particular environmental conditions and high fruit quality. Because these interaction influences chilling requirements for bud-break, water relations, nutrient uptake, plant size, blossoming, time for fruit set, fruit quality and yield efficiency. Also, both the degree and timing of pruning can affect crop load, fruit size, and fruit quality. Pruning during the dormant winter period resulted in better fruit quality than when pruning was delayed until after fruit set. Early thinning had a positive effect on fruit quality, resulting in larger, firmer fruit with higher sugar levels. However, all these parameters are directly or indirectly affected by the environment. Responses of apple fruit to different environmental conditions (temperature, rainfall, relative humidity of the atmosphere and various soil types) was given prior consideration before starting fruit culture in some location. Even though growing conditions (environmental and cultural factors) influence cultivar performance, this can be well compensated by different cultural practices required for appropriate orchard management such as tree training and pruning, use of artificial dormancy breaking chemicals (Dormex, Winter oil and others) to promote flowering and fruit setting as well as for better yield of cultivars by overcoming the influence of fluctuating temperature that would result in incomplete or partial chilling. Cultivar introduction must be based on its temperature requirements (i.e. low, medium or high) for successful orchard establishment. In most of the tropical highland conditions where apple is growing, introducing low-chill cultivar is recommended for quality fruit production because these cultivars are easily satisfied by the existing low temperature and able to tolerate temperature fluctuation in most of the highland areas. Alternatively, medium chill-requiring cultivars were supposed to grow when supported by hand defoliation followed by dormancy breaking agents better yield with good fruit quality. This review mainly focuses on increasing awareness of the impact of environmental influence on apple fruit tree physiology and how to find out solutions for effective orchard management practices in Ethiopia/tropical highlands for quality and sustainable fruit production.