However, under some conditions such as severe pruning, destruction of part of the vine, or boron deficiency, it is possible for two or all three of the buds to produce shoots in spring (Winkler et al., 1974). The secondary bud can be thought of as a “backup system” for the vine normally, it grows only when the primary bud or young shoot has been damaged, oftentimes from freeze or frost in spring. In most cases, only the primary bud grows, producing the primary shoot in the following season. Dormant buds that develop under unfavorable conditions (shade of a dense canopy, poor nutrition, etc.) produce fewer flower cluster primordia for the following season. Bud fruitfulness (potential to produce fruit) is a function of the variety, environmental conditions, and vineyard production practices. They generally will be less fruitful (have fewer and smaller clusters) than the primary bud. Reflecting the sequence of development, the secondary and tertiary buds are progressively smaller and less developed. The flower cluster primordia thus represent the fruiting potential of the bud in the following season. If it is produced under favorable environmental and growing conditions, it will contain flower cluster primordia before the end of the growing season. The primary bud develops first therefore it is the largest and most fully developed by the time the bud goes dormant. The three growing points of the compound bud each produce a rudimentary shoot that ultimately will contain primordia (organs in their earliest stages of development) of the same basic components that comprise the current season’s fully grown shoot: leaves, tendrils, and in some cases flower clusters. During that prior season, it undergoes considerable development. The dormant bud initiates the year prior to its growth as a shoot. It is called dormant to reflect the fact that it does not normally grow out in the same season in which it develops. The dormant bud is the focal point during dormant pruning, since it contains cluster primordia (the fruit-producing potential for the next season). As the bud develops, it follows the pattern of nomenclature as the buds on the shoot: the primary growing point is the axillary bud of the lateral bud the secondary and tertiary growing points are the axillary buds of the first two bracts of the primary growing point. These three buds are packaged together within a group of external protective bud scales within the compound bud. The distinction between secondary and tertiary buds is sometimes difficult to make when observing the bud visually and is often of little importance, so it is common to refer to both of the smaller buds as secondary buds. Photo by Patty Skinkis, Oregon State University.Īlthough the dormant bud (sometimes called an “eye”) looks like a simple structure, it is actually a compound bud consisting of three growing points, sometimes referred to as the primary, secondary, and tertiary buds within one bud. The three buds within the compound bud can be seen.
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