We propagated manchurian lilac (Syringa pubescens subsp. patula ‘Miss Kim’) vegetatively from stem cuttings using overhead mist, submist, and combination propagation systems. Cuttings were collected when terminal buds were already set, after the period of tender growth that is optimal for lilac propagation. Net photosynthesis (Pn) was recorded to assess whether differences in rooting could be attributed to differences in photosynthetic activity of cuttings within each system. The propagation environment differed significantly among systems, with vapor pressure deficit (VPD) substantially greater for submist systems than for overhead mist or combination systems, and root zones warmer in submist and combination systems than in overhead mist. Pn of cuttings did not differ among systems and was initially low, but increased about when the first root primordia were visible. Rooting percentages were 90% among cuttings in the combination system, with cuttings in overhead mist and submist rooting at lower, but similar, percentages (68% and 62%, respectively). Cuttings in the combination and submist systems produced significantly more and longer roots than those in the overhead mist system, and retained nearly all of their leaves. Overall, the use of systems that provide intermittent mist to the basal end of each cutting was effective for propagating manchurian lilac. Our results demonstrate that cuttings in submist alone experience a much greater VPD than those in overhead mist, but may nonetheless root at comparable percentages and produce superior measures of root system quality. Combination systems show promise for rooting of species like manchurian lilac, because cuttings rooted at high percentages and with consistent root system quality, despite having been collected after the optimal spring period for lilac propagation.
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Olivia Sanchez, Stephanie E. Burnett and Bryan J. Peterson
Craig J. Frey, Xin Zhao, Jeffrey K. Brecht, Dustin M. Huff and Zachary E. Black
The U.S. fresh-market tomato industry faces increasing competition from Mexico, which achieves greater productivity and quality due to the use of protected structures. Protected agriculture is limited in humid, subtropical regions of the United States. Although grower interest in high tunnel production has increased in recent years, systematic high tunnel research has not yet been conducted in subtropical Florida. Additionally, although tomato grafting has shown the potential to overcome biotic and abiotic stresses, research of high-tunnel, grafted tomato production in subtropical conditions is lacking. During this 2-year study (Citra, FL), a side-by-side comparison of open field and high tunnel organic tomato production was conducted using a split-split plot design. The most significant benefit of high tunnel production was season extension achieved through the reduction of foliar disease severity, which reduced the area under the disease progress curve by 64% across two seasons. This may be largely attributed to the pronounced reduction in the duration of leaf wetness during the wet months of the growing cycle. Grafting with ‘Multifort’ rootstock reduced the root-knot nematode soil population density by 88% as well as root galling severity, both of which demonstrated the potential for increased levels in the high tunnel production system compared with open field production. The more severe root-knot nematode infestation in high tunnels was likely due to the modification of soil temperatures, which were 2 °C greater during the early part of the season but were reduced after shadecloth application. Compared with the open field, solar radiation was reduced by 23% in the high tunnel before shadecloth application and by 51% after shadecloth application; however, due to the high radiation levels in subtropical Florida, daily light integral levels indicated that light was not limiting for high-quality tomato production. The average wind speed was reduced by 57% in the high tunnel and, together with the reduction in solar radiation, indicated the potential reduction in summer abiotic stress and evapotranspiration within high tunnels. These results revealed that the integrated use of high tunnel and grafting technologies may be important for enhancing fresh-market tomato production in the humid subtropics, especially in organic systems.
Rebecca L. Darnell, Jeffrey G. Williamson, Deanna C. Bayo and Philip F. Harmon
Vaccinium arboreum Marsh is a small tree adapted to low-organic matter soils and is one of the few ericaceous species that tolerates soil pH greater than 6.0. It has a deep root system and is more drought tolerant than cultivated blueberry. The use of V. arboreum as a rootstock for commercial blueberry production has been studied previously in young blueberry plantings. The objective of the current study was to expand on earlier work and evaluate growth, productivity, and tolerance to bacterial leaf scorch (Xylella fastidiosa) in established plantings of own-rooted vs. grafted southern highbush blueberry (SHB). Two field plantings of grafted and own-rooted ‘Meadowlark’ and ‘Farthing’ SHB were established in May 2011: one at the University of Florida–Institute of Food and Agricultural Sciences (UF-IFAS) Plant Science Research and Education Unit in Citra, FL, and the other at a commercial blueberry farm in Archer, FL. At both sites, four rootstock–scion combinations were grown in either pine bark-amended or nonamended soil. Canopy volume was greater in grafted compared with own-rooted ‘Meadowlark’ at both locations throughout the 4 years of the study (2015–18), whereas canopy volume in ‘Farthing’ was not consistently different. For both cultivars and both locations, canopy volume was greater on amended compared with nonamended soil. Although canopy growth was not consistently increased in the grafted compared with own-rooted plants, yield was greater in grafted plants of both cultivars at both locations. Cumulative yield over the 4 years was similar between grafted plants grown on both amended and nonamended soil, and was significantly greater than yield of own-rooted plants on nonamended soil, suggesting the use of this rootstock may decrease the requirement for pine bark amendment. In general, grafted plants produced larger berries, with no negative impacts on fruit soluble solids, titratable acidity, or firmness. ‘Meadowlark’—an SHB cultivar that exhibits high sensitivity to bacterial leaf scorch—displayed decreased development of bacterial leaf scorch symptoms when grafted onto V. arboreum compared with own-rooted plants. These results indicate the potential benefits of grafting SHB onto V. arboreum rootstock, particularly under marginal soil conditions. However, a complete economic analysis that also takes into account any differences in longevity between the two systems must be done to determine whether the benefits of using grafting are feasible financially for the grower.
Jiwei Ruan, Guoxian Wang, Gongwei Ning, Chunmei Yang, Fan Li, Linmeng Tian and Lifang Wu
Strawberry ‘Tokun’ (2n = 10x =70) is a unique cultivar with special flavors, but its late maturity hampers its extension. To advance flowering and fruiting of this decaploid strawberry, the effects of short-day combined with extra nitrogen (N) nutrition treatments on strawberry ‘Tokun’ plants were studied. Runner plantlets of strawberry ‘Tokun’ were harvested and rooted in tray plugs in June 2016, 2017, and 2018, and established plants were conditioned with short-day (SD; 10 hours) and extra N nutrition. The conditioned plants were transplanted into a tabletop substrate culture system in a plastic greenhouse on 27 Aug., 3 Sept., and 10 Sept. during the 3 years, respectively, and the plants received full-element nutrient solution through the drip tube during the whole experimental period. The number of runners and lateral buds, flowering and fruiting periods, and fruit yield were investigated. Longer duration (6–7 weeks) of the SD treatment (10 hours) could significantly reduce the number of runners and increase the number of lateral buds of strawberry ‘Tokun’, advance flowering and fruiting, and achieve a fruit yield of ≈200 g/plant from November to December. The positive effect of extra N nutrition on flowering and fruiting of strawberry ‘Tokun’ was not found. This study is of great practical importance and guiding significance for cultivation and extension of the decaploid strawberry ‘Tokun’.
Cristhian Camilo Chávez-Arias, Sandra Gómez-Caro and Hermann Restrepo-Díaz
Physalis peruviana L. crops are exposed to different stress conditions that limit their productivity. Within these conditions, abiotic stress caused by water and biotic stress by Fusarium oxysporum f. sp. physali (Foph) are frequent at commercial levels. The foliar application of synthetic elicitors can be a tool to mitigate the negative impacts of these stresses. The objective of this study was to evaluate the interaction between Foph inoculation and three foliar applications of brassinosteroids (BR), salicylic acid (SA), and a commercial elicitor based on botanical extracts (BE) of Echinacea purpurea, Potentilla erecta, and Aloe vera on the physiological [stomatal conductance (g S), leaf water potential (Ψwf), chlorophyll fluorescence, and growth] and biochemical [photosynthetic pigments, malondialdehyde (MDA) production, and proline content] responses of cape gooseberry plants subjected to a 6-day waterlogging period. The established treatments were as follows: 1) waterlogged plants without Foph; 2) waterlogged plants with Foph; 3) waterlogged, noninoculated (Foph−) plants treated foliarly with BR, SA, or BE; and 4) waterlogged, inoculated (Foph+) plants treated foliarly with BR, SA, or BE. The results showed that the foliar application of BR or SA reduced vascular wilt development in plants subjected to a hypoxia period. In addition, three applications of BR, SA, or BE favored g S, Ψwf, growth, and chlorophyll fluorescence parameters in cape gooseberry plants under the interaction between Foph and oxygen deficit in the soil. Also, higher photosynthetic pigment and proline contents were observed in plants treated with elicitors under stress combination, whereas a lower MDA production was evidenced in this group of plants. In conclusion, BR, SA, or BE can help mitigate the negative effects of the simultaneous occurrence of Foph and a waterlogging condition for 6 days in cape gooseberry plants.
Enrique I. Sánchez-González, Adriana Gutiérrez-Díez and Netzahualcóyotl Mayek-Pérez
The blooming behavior of the avocado Persea americana Mill. is a sophisticated mechanism that prevents effective self-pollination, enables close pollination, and encourages cross-pollination. However, there is no information on outcrossing rate among Mexican race avocado genotypes (P. americana var. drymifolia Schltdl. & Cham.). Therefore, the objective of this study was to assess the outcrossing rate and genetic variability in progenies of Mexican race avocado genotypes by simple sequence repeat (SSR) and intersimple sequence repeat (ISSR) markers. SSR marker analysis showed a considerable genetic differentiation among avocado families [total expected heterozygosity (He) = 0.540], whereas the total heterozygosity value observed (Ho = 0.098) showed the presence of genetic structure per family. The total Nei’s unbiased average heterozygosity (nHe) value found with ISSR markers was 0.482. The results of the analysis of molecular variance (AMOVA) combining both type of markers showed that genetic variation within avocado families was 58.6%, and among families was 41.6% (P < 0.0001). The outcrossing population rate in P. americana var. drymifolia was 0.774 ± 0.091 (sd), and the ‘Criollo 3’ and ‘Plátano Temprano’ families showed the lowest (–0.083 ± 0.031) and highest (0.814 ± 0.060) outcrossing rates, respectively. Variability in outcrossing rate depends on many factors, including edaphoclimatic, agronomic, and genetic, and needs to be considered to define strategies for the conservation and genetic improvement of outstanding native genotypes. SSR and ISSR markers are useful for estimating genetic variability within and among families of avocado, as well as for determining the outcrossing rates among closely related individuals and with a rather small sample size.
José Luis Chaves-Gómez, Alba Marina Cotes-Prado, Sandra Gómez-Caro and Hermann Restrepo-Díaz
Vascular wilt caused by Fusarium oxysporum f. sp. physali is the most limiting disease in cape gooseberry crops. The use of natural products such as organic additives is a promising alternative for management of this disease. The present study sought to evaluate the physiological response of cape gooseberry plants infected with this pathogen and treated with the organic additives chitosan, burned rice husks, or their mixture. The test was conducted under greenhouse conditions and soil was inoculated with F. oxysporum f. sp. physali strain Map5. Chitosan was applied to seeds and seedlings at the time of transplantation, whereas burned rice husk was incorporated into the soil in a 1:3 ratio. Plants inoculated and not inoculated with the pathogen were used as controls. The following variables were evaluated: area under the disease progress curve (AUDPC), leaf water potential, stomatal conductance (g S), leaf area (LA), dry matter accumulation, photosynthetic pigment contents, proline synthesis, and lipid peroxidation estimation [malondialdehyde (MDA)]. The results showed that cape gooseberry plants with vascular wilt and treated with chitosan had higher g S, leaf water potential, LA, dry matter accumulation, and proline content values. In addition, the levels of vascular wilt severity decreased in comparison with pathogen-inoculated controls. The results suggest that chitosan applications on cape gooseberry plants may be considered as an alternative in the integrated management of the disease in producing areas, because they can mitigate the negative effect of the pathogen on plant physiology.
Isaac T. Mertz, Nick E. Christians and Adam W. Thoms
The branched-chain amino acids (BCAA) leucine (L), isoleucine (IL), and valine (V) are synthesized in plants and are essential to growth in most organisms. These compounds can be absorbed by the plant when foliarly applied, but plant catabolism of BCAA is not completely understood. A recent study observed that BCAA applied in a 2:1:1 or 4:1:1 ratio (L:IL:V) increased creeping bentgrass (Agrostis stolonifera) shoot density compared with applications of equal urea nitrogen (N) at 3.03 lb/acre N. The present study investigated whether those increases could translate to a quicker establishment rate of creeping bentgrass grown from seed in standard greenhouse pots. The BCAA applications were compared with equal N applications using urea and a commercially available amino acid product. All N treatments were applied at 3.03 lb/acre N, per application and applied a total of four times on a 14-day interval starting 14 days after seeding. Measurements included final shoot density counts and root and shoot weights, as well as digital image analysis of percent green cover for each greenhouse pot every 7 days. No differences were observed after 70 days in shoot weight, or percent green cover between BCAA treatments and urea; however, BCAA 2:1:1 and 4:1:1 increased shoot density 21% and 30%, respectively, compared with urea, and were equal to the commercially available amino acid product. Applications of BCAA 4:1:1 also increased creeping bentgrass rooting weight by a factor of 7 compared with urea N.
Furn-Wei Lin, Kuan-Hung Lin, Chun-Wei Wu, Yu-Sen Chang, Kuan-Hung Lin and Chun-Wei Wu
Plant biostimulants have received increasing attention in recent years because of their positive effects on crop performance and contribution to agro-ecological sustainability. The aim of this study was to determine the influence of betaine and chitin treatments, alone and in combination, on lettuce plants by changes in the morphology and physiology of plants exposed to regulated deficit irrigation (RDI). Plants were subjected to full irrigation (FI; no water deficiency treatment, field capacity >70%) and RDI (field capacity <50%) conditions until the end of each experiment. We recorded plant yield–related traits, net photosynthesis, and water use efficiency (WUE) values weekly for 4 weeks and carried out three individual experiments to assess the efficacy of biostimulant and irrigation treatments. Betaine (0, 50, and 100 mm/plant) was foliar-treated every 2 weeks during Expt. 1, whereas chitin (0, 2, and 4 g/kg) was applied to the soil at the beginning of Expt. 2. We then applied the optimal concentration of each chemical alone or in combination to the plants as Expt. 3. Compared with negative control, the application of 50 mm betaine and 2 g/kg chitin significantly increased leaf area (LA) per plant by 48.5% and 25.6%, respectively. Furthermore, 50 mm betaine and 2 g/kg chitin treatment showed a clearly protective effect in RDI plants, enhancing their total fresh weights by 26.10% and 75.0%, respectively, in comparison with control. Comparing WUEyield and WUEbiomass, chemical-treated plants had higher values than control. Betaine (50 mm) or chitin (2 g/kg) treatments alone significantly elevated LA, fresh shoot weight, total fresh and dry weights, net photosynthesis, and WUE values, and boosted the water stress tolerance of lettuce under RDI compared with controls. However, a combined treatment of 50 mm betaine and 2 g/kg chitin did not increase the levels of all yield traits under RDI compared with individual chemical treatment. Most leaves appeared healthy, green, and had visually less leaf chlorosis when treated with chitin or betaine under RDI compared with untreated plants subjected to RDI. Our study indicates that applying betaine and chitin improves plant performance against water supply limitations and highlights their potential for the sustainable production of lettuce.