Breeding Peaches in North America for Cold Hardiness and Perennial Canker ( Leucostomaspp.) Resistance — Review and Outlook

Abstract

Winter injury is an important factor influencing peach ( Primus persica[L.] Batsch) production in North America especially in the northerly areas, and is the major limiting factor affecting the northerly expansion of peach culture (2, 8, 9, 10, 13, 14). Perennial canker is a ubiquitous fungal disease of stone fruits ( Prunusspp.) that is particularly damaging to peaches and nectarines in northerly areas of production except in the arid, irrigated regions of the Pacific north west and southern British Columbia (4, 6, 19, 20). The disease is caused by two facultative wound parasites that enter the tree through dead and dying tissues (4). The causal fungi are Leucostoma cincta(Per. ex Fr.) Hohn (= Valsa cincta) and L. persoonii(Nits.) Hohn ( V. leucostoma). Either or both fungi are involved in the canker disease depending on the geographic region. L. cinctatends to predominate in cooler regions while L. persooniiis more important in warmer regions (4, 12). Many biotic and abiotic factors predispose peaches to perennial canker infection (6, 7, 15, 17, 18, 19, 20) but winter injury appears to be the most important in more northerly areas of production (3, 6, 19, 20). Canker infected trees are commonly observed to be more susceptible to winter injury than healthy ones of the same cultivar. They appear to be especially susceptible to injury from freeze dessication induced by strong drying winds in exposed locations. Usually, the combined influence of low temperature stress and perennial canker is more damaging to peach trees than either acting alone (9). The resultant damage includes injury or death of flower buds, fruit bearing wood, major scaffold limbs and even entire trees (2, 3, 6, 10, 14, 19, 20). Such losses result in greatly reduced yields, shortened orchard life and lower returns to the grower. Losses from winter injury and perennial canker, while not confined to northerly areas, are usually greater there because at the higher latitudes the frequency and severity of low temperature stress is greater than regions further south (13, 14). While hardier peach cultivars with perennial canker resistance will be advantageous in most regions of production, the need for such cultivars is especially urgent in the northern United States and southern Canada. This paper will focus on the progress that has been made in breeding hardier cultivars of peach in North America and will assess the prospects for further genetic improvement of cold hardiness and perennial canker resistance.