Mini Review

Juvenile Period in Plants: A Necessary Tool in Plant Breeding

Florence Mfon Umoh¹*, Ebenezer Lanre Fashoranti² and Emmanuel Imoren¹

¹Rubber Research Institute of Nigeria, Edo State, Nigeria

²Raedial Farm Limited, Benin City, EdoState, Nigeria

Submission: July 16, 2022; Published: August 02, 2022

*Corresponding author: Florence Mfon Umoh, Rubber Research Institute of Nigeria, Edo State, Nigeria

How to cite this article: Florence Mfon U, Ebenezer Lanre F, Emmanuel I. Juvenile Period in Plants: A Necessary Tool in Plant Breeding. Ann Rev Resear. 2022; 7(4): 555720. DOI: 10.19080/ARR.2022.07.555720

Abstract

Plant juvenile period is the period between seed germination and its ability to achieve and maintain flower Hackett [1]. The duration of this period is determined by genetic and environmental factors Kazakov & Kichina [2], and their interaction can produce different plant behaviours Inmaculada et al. [3]. The benefits of traditional breeding practices however, are difficult to achieve in most crops, due to their long juvenile periods thus necessitating long breeding cycles. Two main strategies have been used in fruit breeding programs to overcome these difficulties which include the development of early selection criteria to eliminate genotypes with a long juvenile period and the shortening of this period by means of forced growth of seedlings. However, the length of the juvenile period has agronomic importance due to its relationship with the length of the unproductive period of the new cultivars subsequently reproduced by vegetative cuttings, an important character for fruit trees Inmaculada et al. [3], Experiments have being done on different crops to reduce the juvenile period by manipulating different growth factors and parameters as rapid flowering would hasten conventional breeding and help realize the benefits from genomic selection methods. The objective of this review is to briefly discuss on the juvenile phase of some crops and its effects on the breeding time thus delaying the improvements of those crops.

Keywords: Juvenile phase; Plant breeding; Crop improvement

Background Introduction

Plant juvenile period is the period between seed germination and its ability to achieve and maintain flower Hackett [1]. The duration of this period is determined by genetic and environmental factors Kazakov & Kichina [2] and their interaction can produce different plant behaviours Inmaculada et al. [3]. Plant breeding is an alteration in plants as a result of their use by man, ranging from unintentional changes resulting from the advent of agriculture to the application of molecular tools for precision breeding. It aims at selecting a better type among variants, in relation to yield and quality of edible parts; ease of cultivation, harvest, and processing; tolerance to environmental stresses; and resistance against pests Flavio & Alexandre [4]. The benefits of traditional breeding practices, however, are difficult to achieve in most crops, due to their long juvenile periods thus necessitating long breeding cycles; desired genotypes for a hybridization do not have synchronized flowering due to photoperiod or vernalization requirements, or preferred lines are grown asexually and have limited flowering potential. With the knowledge that plant breeding requires the production of fertile flowers to produce the necessary gametes obtaining such flowers in a synchronized manner and in a practical period can be challenging. Amasino [5]. Thus, seedlings with long juvenile period are not desired by breeder because the first stages of the breeding process are delayed by their assessment De la Rosa et al. [6]. Two main strategies have been used in fruit breeding programs to overcome these difficulties which include the development of early selection criteria to eliminate genotypes with a long juvenile period and the shortening of this period by means of forced growth of seedlings.

Lin et al. [7] emphasized the need to increase he current rate of genetic gain of critical food crops to protect global food security. As the human population presently is around 7.8 billion and is estimated to reach 9.9 billion by 2050 IISD, [8]. Climatic fluctuations (rising temperatures, frequent floods) and drought have been forecasted to lead to novel diseases and frequent pest outbreaks, requiring an agile plant breeding response Hussain et al. [9] Therefore, enhancing the rate of genetic gain depends on accelerated crop breeding pipelines to allow rapid delivery of improved crop varieties. As educed by the breeder’s equation Moose et al. [10]. Plant breeding can be hastened by enhancing factors that influence the genetic gain per unit time Bohra et al; Sinha et al; Varshney et al. [11-13] and importantly, the breeding cycle time Cobb et al. [14]. Since the early 21st century, this suite of Speed Breeding techniques has been applied across economically and scientifically important model, crop and pasture families, including Poaceae, Fabaceae, and Brassicaceae, to achieve up to threefold improvement in annual generation turnover compared to conventional generation advancement systems.

Juvenile phase and the importance of plant breeding in its improvement

The life cycle of higher plants is characterized by two development stages, the vegetative and the reproductive. The former consists of the juvenile and adult vegetative stages. During the juvenile phase, the plants are unable to flower, even under inductive conditions. In certain perennial plants, this period can persist for several decades Amasino Yamagishi et al. [15]. In many fruit crops, this phase before flowering can take more than 20 years Van Nocker & Gardine [16]. However, the length of the juvenile period has agronomic importance due to its relationship with the length of the unproductive period of the new cultivars subsequently reproduced by vegetative cuttings, an important character for fruit trees. Many plants experience an extended juvenile phase before being capable of transitioning to reproductive growth, and this can severely delay the development of new lineages with preferred traits. The switch from vegetative to reproductive development in flowering plant is one of the most important developmental transitions Benedicte Catherine [17] which requires the coordination of developmental and environmental signals.

Photoperiod manipulation in grain amaranth, was reported to be useful in flowering synchronization in several germplasm lines, which, when used with DNA marker technology have led to the development and identification of true hybrids, thus, advancing the breeding program Stetter [18]. Other methodologies to improve generation turnover by promoting early flowering in vegetables involve higher expression of flowering genes. Borovsky et al. [19]; increasing the photoperiod and a foliar mineral supplement have also shown to reduce time to anthesis for a higher generation turnover in oats Tanaka et al. [20]. For the winter pea crop, the manipulation of flowering regulatory genes is a promising way to control key developmental stages, like the dates of floral initiation and flowering as an ideal winter pea should initiate its flower primordia late to avoid frosts, but early to escape drought and heat stresses in late spring. Its correct timing is important in maximizing reproductive success and thus has a major impact on crop performance.

Experiments have been done on different crops to reduce the juvenile period by manipulating different growth factors and parameters as rapid flowering would hasten conventional breeding and help realize the benefits from genomic selection methods. In addition, clonally propagated crops, like banana, roots, and tubers (not fruit crops), are now employing speed breeding to reduce flowering time, increase flowering rate, and the predictability of flowering, for the introduction of disease resistance traits Vira, Souza et al. [21,22] A study was done by De la Rosa et al. [7] on olive seedling to establish useful negative pre selection criteria on the basis of the influence of seedling vigour (measured as plant height or stem diameter) on the characteristics at the adult stage. The results revealed that early evaluation and selection for juvenile period can be performed at the seedling stage in olive progenies on the basis of vigour measurements. Therefore, selection for short juvenile period was valid irrespective of parentage and thus could be efficient in a general context. No correlation existed between juvenile period and yield or fruit traits so this preselection criterion would have no negative effects on these characters.

Pritsa et al. [23] performed an experiment on olive seedling to assess growth traits during the initial developmental stages which could be correlated to time of first flowering, thus, facilitating fast selection in olive breeding programs. It was revealed that pre-selection in olive seedlings for earliness of first flowering is possible, based on vegetative characteristics assessed very early in their development. In the same vain, Rallo et al. [24] studied the relationship between the length of the juvenile period and nine olive seedling parameters (plant height, diameter, number of nodes, lateral shoots, internode length, leaf length, width, area, and shape index) with the aim of selecting the best traits to be used as pre-selection criteria for short juvenile period. It was observed that strong positive correlations existed between the parameters studied. Furthermore, Bagnara [25] performed an experiment on pear seedlings to estimate the relationship between vegetative aspects and early bearing. It was concluded that a short juvenile period in pear is associated with a good efficiency in reserves and dry matter accumulation in woody parts of plant. Leo´n et al. [26] demonstrated that olive seedlings with a short juvenile period will also produce plants with a short unproductive period once vegetatively propagated.

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