Fresh Mass Accumulation Research Articles

Production and postharvest quality of <i>Passiflora edulis</i> Sims under brackish water and potassium doses

<abstract> <p>The aim of this research was to assess the yield and postharvest characteristics of 'BRS Sol do Cerrado' sour passion fruits based on irrigation with varying levels of saline water and potassium fertilization. The study was conducted under field conditions at an experimental farm in São Domingos, Paraíba, Brazil. A randomized block design was implemented in a 5 × 4 factorial arrangement, with five levels of electrical conductivity of water (ECw): 0.3, 1.1, 1.9, 2.7, and 3.5 dS m<sup>−1</sup>, and four potassium doses (KD): 60, 80,100, and 120% of the recommended amount, with 3 replications. The potassium dose equivalent to 120% of the recommended dose in combination with low-salinity water resulted in the highest fresh mass accumulation in the sour passion fruit. Water electrical conductivity up to 2.7 dS m<sup>−1</sup>, along with the lowest recommended KD, led to increased levels of soluble solids and ascorbic acid in the sour passion fruit. Irrigation with water of 3.5 dS m<sup>−1</sup> and using 80 to 100% of the recommended KD enhanced the total sugar content in the sour passion fruit. On the other hand, irrigation with water of 3.5 dS m<sup>−1</sup> combined with 60% of the recommended KD resulted in a higher pulp yield in the 'BRS Sol do Cerrado' sour passion fruit 160 days post-transplantation. Adjustments in potassium fertilization management at different irrigation water salinity levels played a crucial role in maintaining both the production and quality of the sour passion fruit.</p> </abstract>

Physiological, biochemical, and growth aspects in corn inoculated with endophytic bacteria under saline stress

The Caatinga, a Brazilian biome, which has a microbiota with adaptation to both drought and salinity, within this ecosystem are bacteria such as those of the genus Bacillus that stimulate plant growth and increase resistance to biotic and abiotic factors. This study aimed to evaluate the development of corn irrigated with brackish water, through the inoculation of seeds with bacteria isolated from the Caatinga. The experiment was composed of 3 × 4 factorial, with bacteria: T0 (negative control); T1 - bacteria 1 (XX6.9); T2 - mix (XX6.9 + T1.1 and T11.1); and, three salinity levels: (1.5, 2.5, and 4.5 dS m-1) plus control treatment and six repetitions. The following growth analyses were performed at 15 and 54 days after sowing (DAS): plant height, stem diameter, root length, fresh mass, and biochemical analyses: reducing sugars (RS), total soluble sugars (TSS), and the amino acid proline content of leaf and root. The inoculum used increased the growth of the root system, promoting a gain in the accumulation of fresh mass at the beginning of cultivation and reducing its loss at 54 DAS. There was also an increase in carbohydrate accumulation, in addition to the promotion of osmotic adjustment of the cells with the accumulation of the amino acid proline.

Desempenho produtivo e fisiológico de genótipos de jambu cultivados em hidroponia

ABSTRACT Jambu is a condiment herb used in the preparation of typical and herbal dishes in the Amazon Region. The inflorescences, leaves, and stems of the plant are used. In addition, jambu has numerous applications in the cosmetics and food industries due to the presence of the bioactive compound spilanthol. The objective of this study was to evaluate the productive and physiological performance of jambu genotypes of Acmella oleracea, and Acmella ciliata species grown in hydroponics. The experiment used was a completely randomized design with eight treatments and four replicates. The treatments consisted of jambu genotypes (UFR-1, UFR-2, UFR-3, UFR-4, UFR-5, UFR-6, UFR-7 and UFR-8) collected in different locations in the state of Pará. We evaluated the beginning of flowering, length of the main branch, diameter of the main branch, leaf area, shoot fresh mass, inflorescence fresh mass, root fresh mass, total fresh mass, net photosynthetic rate, stomatal conductance, internal CO2 concentration, and instant carboxylation efficiency. The genotypes presented different behaviors about the productive and physiological growth characteristics. The genotypes UFR-1, UFR-2, UFR-3, UFR-4 and UFR-7 exhibited greater precocity of flowering. In general, genotypes of the species A. oleracea presented lower rate of net photosynthesis when compared to those of the species A. ciliata. The genotypes of A. oleracea showed total fresh mass accumulation capacity, in addition to a high potential for inflorescence production. The genotypes UFR-2 and UFR-4 stood out because they presented higher yields of shoots fresh mass and inflorescences, respectively. Therefore, these genotypes should be considered in crop improvement programs.

Lettuce production with rates of biochar from babassu palm rachis

ABSTRACT Use of biochar produced from biomass residues may improve physical, chemical, and biological conditions of soil, reduce greenhouse gas emissions, and increase crop yields. This study evaluated production of lettuce (Lactuca sativa L., cv. Babá de Verão) in a dystrophic Yellow Latosol (LAd) by adding biochar from the babassu palm (Attalea speciosa Mart.) rachis at 0, 10, 20, or 30 t∙ha−1 in pot culture, and growth and production of lettuce evaluated. Lettuce grown with 30 t∙ha−1 of biochar improved plant height, number of leaves, and total fresh mass. Rates that promoted greater accumulation of fresh mass of the aerial part, aerial part dry mass, fresh root mass, root dry mass, and total dry mass ranged between 17.3 and 27 t∙ha−1 of biochar. Use of biochar may be an alternative to improve physical and chemical conditions of LAd soil in successive crops of lettuce in pot culture. The correction of the LAd soil with increasing rates of biochar increased growth and yield of lettuce in pot culture.

Light-Time-Biomass Response Model for Predicting the Growth of Choy Sum (Brassica rapa var. parachinensis) in Soil-Based LED-Constructed Indoor Plant Factory for Efficient Seedling Production.

Little is known about how exactly light plays its role in the growth of choy sum (Brassica rapa var. parachinensis), a widely cultivated vegetable in Asia. By applying a commercial soil using black peat as major constituent with 17:10:14 ratio of NPK fertilizer in this study, the growth responses of choy sum seedling to progressively increasing white LED light intensity in an indoor plant factory were investigated, where positive enhancements were observed in choy sum morphology and growth including both dry and fresh mass accumulation under higher light intensity till 400 μmol/(m2⋅s), then a reduction occurred due to light oversaturation and overheat. In indoor plant factory, the inhomogeneous distribution phenomenon of illumination level was inevitably occurred in indoor farm racks generally. For accurately evaluating the productivity of choy sum grown on such racks, a light-time-biomass response model of choy sum seedling grown at the seedling stage was thus established for the first time, which could reliably predict the production outcome of this species in indoor farming practice under various lighting condition and duration. The robustness of the model was further tested by model variation test and sufficient robustness of this model was confirmed. The new insight obtained for the light-dependence of choy sum growth and the light-time-biomass response model can be used to efficiently direct its seedling production in indoor plant factories.

EFFECTS OF HUMIC SUBSTANCES ON SEED GERMINATION OF WHEAT UNDER THE INFLUENCE OF HEAVY METAL

Introduction. The rapid development of industry in recent decades has caused global pollution, including heavy metals. Of particular danger is the accumulation of heavy metals in plants widely cultivated in crop production practices, such as wheat. Among growth-promoting and remedying drugs, compounds of natural origin — humic substances — deserve special attention. Currently, around the world there is an increased interest in humic substances, the technologies for their production are being improved, and the raw material base is expanding, in which all new types of raw materials are involved. Of particular interest are synthetic humic substances, which are obtained from low molecular weight phenolic precursors. Strict control of the synthesis conditions allows obtaining a product with standardized properties, which is one of the advantages over natural humic substances. In addition, it is assumed that the nature of the low molecular weight phenolic precursor affects the biological activity of the final product. Purpose. The aim of our study was to study the effect of humic substances of various origins (a complex preparation of natural humic substances and synthetic fulvic acids from catechol) on the germination and morphological characteristics of wheat under the influence of heavy metals (Cu 2+ ). Methods. During the study, laboratory, accounting, analytical and mathematical-statistical methods were used. Result. A comparative study of the effect of a complex preparation of natural humic substances and synthetic fulvic acids from catechol on the germination of wheat seeds shows their stimulating effect compared to the control by 11.2% and 8.2%, respectively. The presence in the nutrient solution of Cu 2+ ions at the levels of 0.5, 1 and 5 MPC contributed to the increase of germination energy and germination of seeds in all experiments. The types of humic substances investigated intensify the growth processes in green shoots of wheat. Compared to the control, their length increased by 18.9 - 35.1%. In addition, these substances inhibit the negative effects of Cu 2+ ions even at the level of 5 MPC. Aqueous solutions of Cu 2+ ions have been found to stimulate the formation of primary roots in wheat. At the same time, ions of this heavy metal have a negative effect on root growth, reducing their length by 7.5 times compared to the control. The total length of all roots in wheat plants under the action of different types of humic substances exceeded the control values by 42 - 50%. At the same time, these substances significantly improved root growth when Cu 2+ ions were present in the nutrient solution. The presence of Cu 2+ ions in the solution adversely affected the crude mass of green shoots and roots in the studied wheat plants. However, humic substances improved these indicators compared to the control by 26.8 - 43.3%, which indicates their detoxifying effect. Conclusion. Thus, the treatment of wheat seeds with the studied preparations of natural humic substances and synthetic fulvic acids from catechol activates biological and physiological processes in the seed, thereby affecting the vital activity of the plant at the initial stage of development, affects the formation of additional primary roots and the growth of wheat seedlings. The studied preparations have a positive effect on the accumulation of fresh mass of wheat seedlings, and allow to obtain friendly and uniform seedlings. In addition, under conditions of soil pollution with Cu 2+ ions, various types of humic preparations exhibit phytoprotective properties.

Evaluation of Polyphenolic Compounds and Pharmacological Activities in Hairy Root Cultures of Ligularia fischeri Turcz. f. spiciformis (Nakai).

A considerable amount of bioactive compounds have been used for the biopharmaceutical engineering to help human health and nutrition. Hairy root culture (HRC) or transgenic root is a favourable alternative technique for phytochemical production. Ligularia fischeri is a significant source of pharmaceutically important active compounds with an enormous range of health care applications. HRC of L. fischeri was developed using Agrobacterium rhizogenes for the production of polyphenolic compounds with antioxidant, antimicrobial, antidiabetic, anticancer and anti-inflammatory pharmaceutical activities. Hairy roots (HRs) were selected by morphological assessment, genetic and molecular analyses. The maximum accumulation of fresh mass (94.15 g/L) and dry mass (9.45 g/L) was recorded in MS liquid medium supplemented with 30 g/L sucrose at 28 days. Furthermore, HRs successfully produced numerous polyphenolic compounds, including six hydroxycinnamic acids, seven flavonols, seven hydroxybenzoic acids, vanillin, resveratrol, pyrogallol, homogentisic, and veratric acids, which were identified by UHPLC analysis. HRs produced higher total phenolic (185.65 mg/g), and flavonoid (5.25 mg/g) contents than non-transformed roots (125.55 mg/g and 3.75 mg/g). As a result of these metabolic changes, pharmaceutical activities were found higher in HRs than non-transformed roots (NTRs). The present study indicates that HRC has the potential to increase the content of beneficial polyphenolic compounds with higher potential pharmaceutical activities. To the best of our knowledge, the present study is the first report on enhancing the production of polyphenolic compounds with pharmaceutical activities from the HRCs of L. fischeri.

EFFECT OF CHILLING STRESS ON THE PHOTOSYNTHETIC PERFORMANCE OF YOUNG PLANTS FROM TWO MAIZE (ZEA MAYS) HYBRIDS

: In the climate conditions of Bulgaria, early stages of maize plants development often go under suboptimal temperatures. Chilling stress is known to cause different physiological disturbances in young maize plants during the transition period from heterotrophic to autotrophic nutrition. However, the effect of chilling may differ among maize hybrids. Photosynthetic performance could be a good indicator for the hybrid tolerance to chilling. The aim of our study was to evaluate the tolerance of young maize plants from two hybrids – the new Bulgarian hybrid - Kneza 307 and the hybrid P9528 using as criteria the changes in their photosynthetic performance.Plants at the third leaf stage were exposed for seven days to chilling stress. At the end of the experimental period, growth, leaf lipid peroxidation, and several photosynthetic parameters were measured. We found that chilling stress reduced the fresh mass accumulation, increased lipid peroxidation, diminished net photosynthetic rate and chlorophyll content, and enhanced non-photochemical quenching of chlorophyll fluorescence. Although the responses of both hybrids were similar, some specificity were observed and discussed.

Double sigmoidal models describing the growth of coffee berries

ABSTRACT: This study aimed to verify if the growth pattern of coffee berries, considering fresh mass accumulation over time, is double sigmoid and to select the most suitable nonlinear model to describe such behavior. Data used consisted of fourteen longitudinal observations of average fresh mass of coffee berries obtained in an experiment with the cultivar Obatã IAC 1669-20. The fits provided by the Logistic and Gompertz models were compared in their single and double versions. Parameters were estimated using the least squares method using the Gauss-Newton algorithm implemented in the nls function of the R software. It can be concluded that the growth pattern of the coffee fruit, in fresh mass accumulation, is double sigmoid. The double Gompertz and double Logistic models were adequate to describe such a growth curve, with a superiority of the double Logistic model.

Comparison of the Effects in the Germination and Growth of Corn Seeds (Zea Mays L.) by Exposure to Magnetic, Electrical and Electromagnetic Fields

At the moment of obtaining good agricultural yields, as in the specific case of corn (Zea mays L.), the action of various factors, such as the surrounding environment, can cause a decrease of the germinative power of seeds.To improve the germinative power of the corn seeds, it has been searched for new methods and technologies. In this regard, our study focuses on the comparison of the effects on seeds when exposed to magnetic fields of high and low intensities, and to electric and electromagnetic fields. For a time of 15 days the seeds were exposed by different fields. The studied variables were: the germination percentage, growth dynamics of coleoptiles, and accumulation of fresh mass, dry biomass and contents of chlorophyll a, chlorophyll b, and total chlorophyll. The best results were obtained for the seeds treated with electromagnetic fields doubling the value of most of the indicators under study.

Phenotypic plasticity of Neonotonia wightii and Pueraria phaseoloides grown under different light intensities.

Plants have the ability to undergo morphophysiological changes based on availability of light. The present study evaluated biomass accumulation, leaf morphoanatomy and physiology of Neonotonia wightii and Pueraria phaseoloides grown in full sunlight, as well as in 30% and 50% shade. Two assays were performed, one for each species, using a randomized block design with 10 replicates. A higher accumulation of fresh mass in the shoot of the plants was observed for both species under cultivation in 50% shade, while no differences were detected between the full sunlight and 30% shade. N. wightii and P. phaseoloides showed increase in area and reduction in thickness leaf when cultivated in 50% shade. There were no changes in photosynthetic rate, stomatal conductance, water use efficiency and evapotranspiration of P. phaseoloides plants because growth environment. However, the shade treatments caused alterations in physiological parameters of N. wightii. In both species, structural changes in the mesophyll occurred depending on the availability of light; however, the amount of leaf blade tissue remained unaltered. Despite the influence of light intensity variation on the morphophysiological plasticity of N. wightii and P. phaseoloides, no effects on biomass accumulation were observed in response to light.

Desenvolvimento dos frutos de lulo (Solanum quitoense LAM), em Viçosa-MG

O lulo é um fruto tropical e exótico, originário dos Andes, tem cor laranja quando maduro, e é uma baga globosa, assemelha- se a um tomate, o epicarpo é grosso e coriáceo, sua polpa é verde-clara, pegajosa, ácida e suculenta, contendo muitas sementes. Objetivou-se acompanhar as características físicas, químicas e fisiológicas ocorridas durante o desenvolvimento do fruto de lulo, da antese ao amadurecimento completo, em Viçosa-MG. Os frutos apresentaram um padrão de crescimento sigmoidal simples em resposta à variação do tempo. O desenvolvimento do fruto foi dividido em três fases. A primeira foi até os 7,39 dias após a antese (DAA), sendo caracterizada pela alta taxa respiratória, provavelmente devido à intensa multiplicação celular, e o pericarpo apresentava coloração verde-clara. A segunda fase estendeu-se a partir dos 7,39 até os 57,63 DAA, sendo caracterizada pelas taxas máximas das características estudadas. A taxa respiratória cresceu até 45 DAA, mantendo-se estável até os 52 DAA. A última fase estendeu-se a partir dos 57,63 DAA até os 95,00 DAA. Essa fase foi caracterizada pela estabilização nas dimensões e no acúmulo de massa fresca. Nesse período, ocorreu a ascensão climatérica (dos 52 aos 59 DAA). O climatério respiratório ocorreu aos 66 DAA, com pico de produção de CO2 de 110,99 mg de CO2 kg-1h-1. O pós-climatério ocorreu dos 73 aos 95 DAA, quando houve aumento no teor de sólidos solúveis e queda da acidez titulável e vitamina C da polpa. Nessa fase, o pericarpo dos frutos apresentava-se com coloração alaranjada.

Atrazine metabolism in field-grown maize and the effect of atrazine phototoxicity on yield

Maize was grown under field conditions, applying conventional farming practices. Atrazine was sprayed pre- emergence at concentrations of 1,25 I ha−1ai. and 5 I ha−1ai. Severe phytotoxicity symptoms were visible from the first- to about the sixth-leaf stage i.e. 25–30 days after planting in the maize plants treated with 5 I ha−1 atrazine. The growth rate of atrazine-treated maize plants was inhibited during this period, whereafter it recovered. No effect on subsequent fresh mass accumulation could be detected when comparing treated plants with the control after about 40–45 days after planting. The inhibition of growth during the early developmental stages had no negative effect on the final yield. Hydroxylation of atrazine as detoxifying mechanism seems to play the major role in the case of root-absorbed atrazine up to approximately 25–30 days after planting.

Long-term maintenance of Pinus nigra embryogenic cultures through cryopreservation

Embryogenic tissues of Pinus nigra have been cryopreserved using a two step slow-freezing method. In the first experiment, 20 cell lines were included and the effect of the duration of cryostorage (1 h vs. 1 year) on regrowth was compared. After a short-term storage (1 h in liquid nitrogen, LN) out of 20 cell lines tested 15 showed regrowth (75%) with individual frequencies 10–100%. Long term storage (1 year in LN) resulted in regrowth of 14 cell lines (70%) while the individual frequencies reached 10–100%. One year storage had no negative influence on the fresh mass accumulation evaluated 2–3 months after thawing. Another 20 cell lines were included in the second experiment with the aim to study the correlation between cryotolerance and maturation capacity of cell lines. Between maturation capacity and cryotolerance expressed as regrowth frequencies of individual cell lines, no correlation has been found.

Regrowth of embryogenic tissues of Pinus nigra following cryopreservation

Embryogenic tissues of a conifer species Pinus nigra Arn. have been cryopreserved by a slow-freezing method. The effect of cryoprotective compounds such as maltose, sucrose or sorbitol (each 0.5 M) combined with 7.5% (v/v) DMSO has been tested. After thawing, the following parameters have been investigated: tissue regrowth 6 weeks after thawing, and post-thaw growth evaluated as fresh mass accumulation as well as genetic stability in post-thaw period. The parameters mentioned have been compared in both cryopreserved and non-cryopreserved tissues. Out of eight cell lines used in experiments, seven survived cryopreservation (87.5% regrowth), although cell line and treatment effects were observed. In most cell lines, sucrose or maltose pretreatments were superior over sorbitol. In the regrown cell lines, the post-thaw growth as fresh mass accumulation was not negatively influenced by cryopreservation. No genetic variation was observed in cryopreserved tissues using a RAPD approach.

Quantifying the dynamics of sugar concentration in berries of Vitis vinifera cv. Shiraz: a novel approach based on allometric analysis

Concentrations of key compounds (e.g. sugar) in berries are the net result of relative changes in the amount of compound per berry and berry size. The complex nature of concentrations is widely recognised, but the widespread use of chronological scales for comparisons implies that ontogenetic drift or size-dependent effects are often overlooked. This paper presents an allometric analysis of sugar concentration in berries of cv. Shiraz as a way to formally account for ontogenetic drift. Our starting point is the double-sigmoid growth pattern of a grape berry where we distinguish Phase 1, from flowering to veraison; Phase 2, from veraison to peak berry fresh mass, and Phase 3, after peak fresh mass. Phase 3 explicitly accounts for the late season shrinkage typical of Shiraz berries. We advance an allometric model of sugar per berry with berry fresh mass, rather than time, as descriptor. The condition for an increase in sugar concentration in Phase 2 is that the relative rate of sugar accumulation per berry (RSB) exceeds the relative rate of berry net accumulation of fresh mass (RFM). This is equivalent to an allometric coefficient, calculated as the slope of the regression between amount of sugar per berry and berry mass in a log-log scale, being greater than 1. For Phase 3, the condition for increase of sugar concentration is that a large reduction in berry mass offsets any putative change of sugar per berry, yielding an allometric coefficient < 1. Such an allometric model was tested against measured data from sixteen contrasting crops resulting from the combination of eight water regimes and two seasons. Berry mass peaked between 96 and 105 days after anthesis, and these dates were used to separate Phases 2 and 3. In Phase 2, the relative rate of increase in sugar per berry varied from 0.01 to 0.02 d-1 in comparison to the relative rate of increase in berry fresh mass that varied from 0.0038 to 0.0066 d-1. Sugar per berry thus increased 2.4–3.3 times faster than berry mass, with allometric coefficients between 1.98 and 2.91 accounting for 78% of the variation in the relative rate of change of sugar concentration. In Phase 3, the relative rate of change in sugar per berry was not different from zero (P 0.05) in most cases, whereas the rate of change in berry size ranged from –0.0013 to –0.0035 d-1 and was significant (P < 0.05) in 14 out 16 cases. The small changes in sugar per berry and the net loss of berry material yielded allometric coefficients between 0.17 and 1.11, which accounted for 72% of the variation in the relative rate of change in sugar concentration. We conclude that a model, which pivots around peak berry mass, with allometric coefficients above 1 in Phase 2 and below 1 in Phase 3, is suitable to quantitatively account for ontogenetic drift in the dynamics of sugar concentration in berries of Shiraz. This allometric approach demonstrated that sugar per berry during the stage of berry shrinkage is a plastic trait under significant environmental influence. For the same genotype, environmental conditions could determine either, a putative backflow of water accounting for net loss of berry fresh mass (RFM < 0) that could also carry some sugar from berries back to the parent vine (RSB < 0) or a small gain of sugar (RSB 0) closely coupled with a net loss of berry fresh mass (P= 0.003).

Disponibilidade de água no solo e crescimento de artemísia

Plantas de artemísia (Tanacetum parthenium L. Schultz-Bip.), cultivadas em vasos com substrato mantido na capacidade de campo, a 90%, a 70% e a 50% da capacidade de campo foram comparadas quanto à altura, acúmulo de massa fresca na parte aérea, teor relativo de clorofila e teor de prolina. O teor relativo de clorofila foi estimado por meio do clorofilômetro SPAD-502, enquanto o teor de prolina foi determinado por colorimetria. Verificou-se reduções de 16% na altura e de 22,5% no acúmulo de massa fresca nas plantas crescidas a 50% da capacidade de campo, em relação àquelas crescidas a 90% da capacidade de campo. O teor relativo de clorofila nas folhas, em quaisquer dos níveis hídricos, decresceu com o tempo, indicando tendência à senescência. Apesar da redução contínua nos níveis de clorofila, as plantas mantidas a 50% da capacidade de campo tiveram, durante todo o tempo acompanhado, teor relativo de clorofila cerca de 30% mais alto comparado às plantas mantidas a 90% da capacidade de campo. O teor de prolina também foi maior nessas plantas, indicando ocorrência de estresse por deficiência hídrica e ajuste osmótico. O maior teor relativo de clorofila e de prolina nas folhas expandidas das plantas sob deficiência hídrica pode ser utilizado como indicativo de estresse.

Fruit Mass Development in Three Cranberry Cultivars and Five Production Regions

Fruit mass development in `Crowley', `Pilgrim', and `Stevens' cranberry (Vaccinium macrocarpon Ait.) was compared in five states for two seasons. Comparing all locations, `Stevens' and `Pilgrim' cranberries had similar growth curves with a faster growth rate than that of `Crowley'. Regional differences in fruit development were observed. Shorter growing seasons, especially in Wisconsin, were compensated for by more rapid growth rates. Conversely, low initial mass and slower growth rates were compensated for by the longer growing season in the Pacific Northwest. Solar radiation intensity accounted for little of the variability in fruit growth. Neither growing degree days nor numbers of days were good predictors of cranberry fruit fresh mass accumulation. Instead, numbers of moderate temperature days (between 16 and 30 °C) appeared to be key, accounting for greater than 80% of the variability in cranberry fresh biomass accumulation. The most rapid growth rates occurred when temperatures were in this range. High temperatures were limiting in New Jersey while low temperatures were limiting in Oregon and Washington. In one of two seasons, low temperatures were limiting in Wisconsin: accumulation of 0.5 g fresh mass took 11 d longer. Massachusetts had the fewest periods of temperature extremes in both seasons, resulting in the shortest number of days required to accumulate 0.5 g fresh mass.

The phytotoxicity of selected mycotoxins on mature, germinatingZea mays embryos

Mature maize (Zea mays) embryos were exposed to 5, 10 and 25 µg ml(-1) of deoxynivalenol (DON), zearalenone (ZEA), ochratoxin A (OA) and a mixture of zearalenone and deoxynivalenol (ZEA/DON) for 9 days. DON and the ZEA/DON combination were consistently more inhibitory of the measured parameters than either ZEA or OA. Based on the predicted additive values, it would appear that, in combination, ZEA and DON act synergistically to inhibit root and shoot growth. For ZEA alone, a concentration of 5 µg ml(-1) ZEA was generally inhibitory of root and shoot elongation and fresh mass accumulation, while at 10 and 25 µg ml(-1), this toxin had a stimulatory effect on these parameters. For OA, the measured effects on root and shoot growth at 5 and 25 µg ml(-1) were stimulatory, while at 10 µg ml(-1) OA, an inhibitory effect was observed. For all toxins, inhibitory/stimulatory effects were generally more marked for root parameters than for shoot elongation or mass.

Aflatoxin B1--its effects on an in vitro plant system.

The phytotoxic effects of aflatoxin B1 (AFB1) on in vitro cultures of differentiating calli and regenerating plantlets of Nicotiana tabacum were assessed. Callus appeared more sensitive to the effects of AFB1, with fresh mass accumulation and callus chlorophyll levels affected at low (approximately 0.5 micrograms/ml) aflatoxin concentrations. Transmission electron microscopy revealed early deteriorative alterations in chloroplast morphology. Inhibitory effects of the toxin (up to and including 10 micrograms/ml) on callus fresh mass accumulation were reversed following a 3 week toxin-free recovery period. In tobacco plantlets, root and leaf development, and root and leaf mass were significantly inhibited in a dose-dependent fashion with increasing AFB1 concentration above 0.5 micrograms/ml. Inhibitory effects on plantlet root development were more pronounced that on leaf development.