Mechanical Stimulation Modifies Canopy Architecture and Improves Volume Utilization Efficiency in Bell Pepper: Implications for Bioregenerative Life-support and Vertical Farming

Abstract

Open Agriculture. 2017; 2: 42-51 vertical system requirements or by expanding the species range that can be grown in a fixed production volume. Mechanical stimulation is also discussed as a microgravity countermeasure for crop plants.Keywords: Thigmomorphogenesis, Plant Dwarfing, Capsicum annum 'California Wonder', Advanced LifeSupport, Vertical Agriculture IntroductionIt has long been recognized that mechanical stimulation (MS; stress), such as wind action, rubbing, constriction, shaking, and encounters with physical barriers can have a dramatic influence on plant morphological development (Biddington 1986, Darwin 1880, Jaffe 1973, Mitchell et al. 1975, Mitchell 1977. Jaffe (1973) demonstrated that daily MS to partially mature internode tissue, applied by rubbing stem tissue between two fingers, could induce dramatic reductions in internode length resulting in dwarf phenotypes in a range of crop species. Jaffe (1973) coined the term thigmomorphogenesis, (thigma being the Greek word for touch) to describe these long term morphological responses to touch. Over the ensuing 40 years many others have followed up on Jaffe's work, notably amongst others, Cary Mitchell's group at Purdue (West Lafayette, IN, USA), Joyce Latimer at Virginia Tech (Blacksburg, VA, USA), and Janet Braam at Rice University (Houston, TX, USA). It is now known that thigmomorphogenesis includes a wide range of responses including, but not limited to, shortening of internodes, stem thickening, reduced leaf expansion, changes in chlorophyll content, and alterations in plant hormone levels (Beyl & Mitchell 1983, Biddington 1986, Braam 2005, Chehab et al. 2008, Latimer et al. 1991, Mitchell & Myers 1995, Monshausen & Haswell 2013. Abstract: Mechanical stimuli or stress has been shown to induce characteristic morphogenic responses (thigmomorphogenesis) in a range of crop species. The typical mechanically stimulated phenotype is shorter and more compact than non-mechanically stimulated plants. This dwarfing effect can be employed to help conform crop plants to the constraints of spaceflight and vertical agriculture crop production systems. Capsicum annum (cv. California Wonder) plants were grown in controlled environment chambers and subjected to mechanical stimulation in the form of firm but gentle daily rubbing of internode tissue with a tightly wrapped cotton swab. Two studies were conducted, the first being a vegetative growth phase study in which plants were mechanically stimulated until anthesis. The second study carried the mechanical stimulation through to fruit set. The response during the vegetative growth experiment was consistent with other results in the literature, with a general reduction in all plant growth metrics and an increase in relative chlorophyll (SPAD) content under mechanical stimulation. In the fruiting phase study, only height and stem thickness differed from the control plants. Using the data from the fruiting study, a rudimentary calculation of volume use efficiency (VUE) improvements was conducted. Results suggest t...

Breeding new varieties for controlled environments

“…). Some plant varieties have been shown to respond to touch, leading to a shorter plant that could possibly be controlled by a mechanical stimulus (Graham & Wheeler ).…”

“…Stem elongation, whether hypocotyl elongation or internode expansion, is sensitive to light control, as is coleoptile expansion (Parks et al 2001;de Wit et al 2016). Some plant varieties have been shown to respond to touch, leading to a shorter plant that could possibly be controlled by a mechanical stimulus (Graham & Wheeler 2017).…”