Young Corn Plants Research Articles

Organoleptic Quality and pH of Silage of Young Corn and Sorghum

Effective processing of young corn and sorghum silage can be evaluated based on physical attributes like fragrance, colour, texture, and the properties and transformations that happen in the feed during the ensiling process. These attributes can be employed to assess and establish the quality of the feed. The purpose of this research is to determine the characteristics of young corn and sorghum silage by conducting pH testing and organoleptic analysis. The study used three types of silage: P1 - young corn, P2 - sorghum, and P3 - a mix of young corn and sorghum. The variables examined included colour, aroma, texture, presence of fungi, and pH. The data indicates that the silage produced from young corn and sorghum plants was of high quality. The feed before the silage production process was the same shade, and the end product had a sour scent. Texture-wise, the majority of the silage was slightly rough and not slimy, with no signs of fungal contamination. The pH ranged from 3.63-3.92, confirming the silage's acidic nature. Silage made from young corn and sorghum plants exhibits organoleptic qualities such as a brownish-green hue, mildly fragrant aroma, slightly mushy consistency, and no detected presence of fungus. Moreover, due to its acidic properties resulting from the pH value, it is highly conducive for the proliferation of lactic acid bacteria.

Influence of the site of oviposition on the level of egg parasitism in the corn leafhopper, Dalbulus maidis (Hemiptera: Cicadellidae).

The corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), transmits three important plant pathogens that adversely affect corn crop and ranges from the USA to Argentina. The vector has a rich natural enemy complex that generates high levels of parasitism, but its populations are persistent and prevalent. We characterized the oviposition sites of D. maidis on young corn plants in order to verify the hypothesis that the vector has an oviposition strategy for mitigating parasitism. Oviposition locations on plants were assessed in the laboratory and eggs within corn plants were exposed to natural parasitism in a cornfield. Eggs were located mostly laid in the unfolded leaves and were attacked by five parasitoid species. Parasitism was significantly affected by the class of leaf and the position of the egg in the leaf. Anagrus virlai Triapitsyn was the most abundant parasitoid species, which emerged significantly higher in the basal blade than other species. Our results suggest that leafhoppers minimize egg parasitism by laying their eggs within concealed locations on the plant.

Review of Pythium Species Causing Damping-Off in Corn

Seedling blights and root rots caused by Pythium species account for almost US$25 million in annual losses to corn (Zea mays) production in the United States and Ontario. Variations in annual rainfall and increasing use of no-till agriculture can favor soilborne pathogens like Pythium. To date, 44 species have been reported as pathogenic to corn in the United States. The average annual corn planting date in the United States has shifted approximately 1 week earlier in the past decade, exposing young corn plants to longer germination periods of generally cooler temperatures, favoring attack by Pythium. Optimal temperatures, aggressiveness, and response to chemical and biological treatment options vary by species. This review consolidates the species of Pythium reported as corn pathogens in literature to date. It also provides an insight into management strategies and discusses variations in fungicide sensitivity observed in corn-related Pythium species.

Combined Starter Phosphorus and Manure Applications on Silage Corn Yield and Phosphorus Uptake in Southern BC

Phosphorus (P) management using mineral and manure P in excess of plant needs contributes to legacy soil P in coastal British Columbia, Canada. The objectives of this study were (a) to assess the effects of starter P at early growth stages and their carryover through corn maturity, and (b) to determine how corn yields relate to soil P saturation indicators. Eleven 1-year experiments were conducted on sites with contrasting legacy soil P in 2018 (three sites) and 2019 (eight sites). Six combinations of starter and manure P rates (T1: 0Pstarter + 0Pmanure; T2: 0Pstarter + 35Pmanure; T3: 5Pstarter + 30Pmanure; T4: 10Pstarter + 25Pmanure; T5: 15Pstarter + 20Pmanure; T6: 20Pstarter + 15Pmanure) were assigned to a RCBD with four replicates. In 2018, corn dry matter weight (DMW) at the 6-leaf stage was affected by starter P in all sites, and the response curve was described by a linear-plus-plateau model with critical starter P of 5 and 7.5 kg ha 1. In 2019, corn DMW at early growth stages was not affected by starter P. Corn DMW at harvest varied between 15.15 Mg ha–1 in sites with low initial soil P and 27.20 Mg ha–1 in sites with excess P. Four sites exhibited a trend of high DMW with treatment comprising low starter P and high side-dressed manure P additions. The degree of P saturation (DPS, 14% to 38%) and P saturation index (PSI, 3% to 14%) were related to corn DMW by quadratic functions (R2 = 0.76 - 0.94). From these results, we can conclude that the effect of starter P on young corn plants varies with year, but does not carryover through harvest. Moreover, current starter P (30 - 40 kg ha–1) recommended for corn can be reduced by up to 75% (5 - 7.5 kg ha–1) without affecting yield, thus reducing annual P inputs and farmers’ production costs. Finally, PSI as a proxy of DPS is a possible agro-environmental indicator that, coupled with reduced starter P fertilizer, can further contribute to reducing the risk of P transfer from agricultural soils in coastal British Columbia.

Adaptive reactions of corn plants to acute ultraviolet radiation

Aim. The goal of this work was to study the adaptive reaction of young corn plants (Zea mays L.) to the action of acute ultraviolet B (UV-B) radiation in the vegetative growth period. Methods. Corn plants hybrid Dostatok 300 MV in the phase of two leaves were irradiated by UV-B at doses of 1, 2, 4, 8, 16 kJ/m2 with a power of 6 W/m2 and were grown in a long day conditions. After irradiation, the growth of shoots in length, the growth of the mass of plants, the content of photosynthetic pigments and endogenous hydrogen peroxide (HP) in the leaves were determined. Results. It is shown that after irradiation of corn plants UV-B at doses of 4, 8, 16 kJ/m2 the growth of shoots in length decreased, after the irradiation of UV-B at doses of 1, 2 kJ/m2 mass of plants increased. UV-B irradiation in all doses, except for a dose of 16 kJ/m2, stimulated the accumulation of photosynthetic pigments in the leaves. Increasing HP content in the leaves was determined in corn leaves after irradiation of UV-B in all doses. Conclusions. It is shown that irradiation of young corn plants by acute UV-B at doses from 1 to 16 kJ/m2 induced adaptive reactions, that included inhibition of shoot growth with simultaneous stimulation of plants mass growth, accumulation of photosynthetic pigments, increased endogenous content of HP. The adaptive period lasted about 10 days, after that processes of growth, formation of a photosynthetic apparatus and content of HP were stabilized. UV-B belongs to the necessary components of sunlight components for corn growth. Keywords: UV-B radiation, Zea mays L., photosynthetic pigments, adaptation.

Evaluation of the growth of young corn plants grown in different types of soil

Corn is a crop of great national importance, being the second most produced grain in Brazil. However, their yield is affected, among other factors, by soil fertility. The objective of this work was to evaluate the initial growth of two cultivars of maize cultivated in different types of soil. The experiment was conducted in the form of a randomized block design, in a factorial scheme two maize cultivars (Pioneer and Bandeirantes) x 3 soil types (clayey, mixed and black soil), with eight replications each. The height and diameter of the stem were evaluated weekly. The dry mass of the aerial part (MSPA), roots (MSR) and total (MST), as well as the MSPA / MSR ratio, were evaluated 21 days after emergence of the seedlings. For the height and diameter data, regression analysis was performed at a 10% probability level. For the other variables, we analyzed the factorial variance at x b at the 5% probability level. The software BioEstat version 5.3 was used. It was observed that T1 and T2, for both cv. of maize, obtained the highest results for stem height and diameter, MSPA, MSR, MST and MSPA / MSR ratio. Regarding the cultivar, Pioneer was superior to Bandeirantes for the variables MSPA, MST and MSPA / MSR ratio. Therefore, clayey and mixed soils were superior to black soil, favoring the initial development of corn plants.

Adaptation of corn plants to chronic ultraviolet irradiation

Aim. The adaptation of young corn plants (Zea mays L.) to the effect of chronic ultraviolet B (UV-B) irradiation during vegetative growth and formation of photosynthetic apparatus of leaves was studied. Methods. Corn plants hybrid Dostatok 300 MB in the phase of two developed leaves was irradiated with UV-B in dose of 2 kJ/m2 per day with a power of 1 W/m2 in long day conditions during 12 days. During this period, the growth of plants was measured, content of photosynthetic pigments and endogenous hydrogen peroxide (HP) was determined in the leaves. Results. It was established that the effect of chronic UV‑B irradiation caused the temporary inhibition of leaf growth, synthesis of photosynthetic pigments and increasing of HP content in them. Then the growth processes and pigment complex recovered to the level of no irradiated plants and exceed it, indicating the induction of adaptive reactions in young corn plants. Conclusions. It was shown that the effect of a low dose of chronic UV-B irradiation caused a delay in growth processes and the formation of a photosynthetic complex with subsequent adaptation to stress in young corn plants. Keywords: UV-B irradiation, Zea mays L., photosynthetic pigments, adaptation.

SWEET CORN CAROTENOID CONCENTRATIONS INFLUENCED BY HERBICIDE APPLICATIONS

Carotenoids serve antioxidant functions in plant photosynthetic processes, as well as in actions of disease reduction in mammalian systems. Lutein and zeaxanthin are important dietary carotenoids in suppressing aging eye diseases. Age-related macular degeneration now affects more than 1.75 million individuals in the US. Sweet corn (Zea mays var. rugosa) is one of only a few vegetable sources high in zeaxanthin. Mesotrione herbicide is currently labeled for selective pre- and post-emergence weed control in sweet corn production. Mesotrione competitively inhibits phytoene desaturase, a critical enzyme in carotenoid biosynthesis, which results in bleaching of leaf tissues in susceptible species and eventual plant death. Sweet corn is tolerant to mesotrione applications; however, differing sensitivity exists among genotypes. What remains unclear is the impact of mesotrione on carotenoid concentrations in mature sweet corn kernels following post-emergent applications to young corn plants. Our research objective was to measure mature kernel carotenoid concentrations in response to post-emergence applications of mesotrione to genotypes of different sensitivities. Post-emergence treatments included mesotrione applied alone, or in mixtures with the photosystem II inhibitor atrazine applied to corn plants of either 5-10 or 15-20 cm in height. Kernels were harvested from mature plants and measured for carotenoid concentrations. Mesotrione applied alone, or in mixtures with atrazine acted to increase concentrations of kernel antheraxanthin, lutein, and zeaxanthin in several sweet corn genotypes. Mesotrione applications resulted in greater pools of kernel carotenoids once the sweet corn genotypes overcame initial herbicidal photo-oxidative stress. This is the first report of herbicides directly up regulating a key biochemical pathway linked to the nutritional quality of a vegetable crop.

Mode of Action and Genetic Analysis of Resistance to Fluazinam in Ustilago maydis

AbstractUstilago maydis strains, with low to moderate resistance to fluazinam (Rf ranging from 11.8 to 80), were isolated in a mutation frequency of 0.75 × 10−7 after chemical mutagenesis with N‐methyl‐N‐nitro‐N‐nitrosoguanidine (MNNG). Genetic analysis resulted in the identification of two chromosomal genes. A study of the effect of mutant genes in the phytopathogenic fitness of U. maydis revealed that the resistance mutations had no apparent effect on mycelia growth rate and pathogenicity on young corn plants. Cross‐resistant studies showed that the mutations for resistance to fluazinam were also responsible for resistance to oligomycin, but not to dinitrophenol. A dose‐dependent inhibition of glucose oxidation in whole cells was observed by both fluazinam and oligomycin, and a complete inhibition was found at 40 μg/ml. The results obtained provide strong evidence that the mode of action of fluazinam consists of the inhibition the fungal cell's energy production process through direct inhibition of the ATP synthetase.

Interaction Effects of Zinc and Manganese on Growth, Uptake Response and Chlorophyll Content of Sweet Corn (Zea mays var. saccharata)

Manganese (Mn) and Zinc (Zn) interact with each other and this interaction can result in impacts on the yield of corn plants. This study was conducted to examine the effect of different levels of Mn and Zn on the yield, Mn and Zn concentration, root growth parameters and chlorophyll contents of corn plants. Sweet corn was grown in nutrient culture containing all combinations of Zn and Mn at levels of 0.0, 0.1, 1.0 and 10.0 mg L-1 as ZnSO4.7H2O and MnSO4.H2O, respectively and harvested at 28 days after transplanting. Mn and Zn concentrations in roots and shoots increased with increasing Mn and Zn concentration in nutrient solution. Zn concentration in both roots and shoots enhanced with increasing Mn levels. Mn concentration in shoots did not show any correlation with Zn concentration in nutrient solution, but Mn concentration in roots decreased with increasing levels of Zn. Zn0Mn1 treatment produced the highest yield. The lowest dry weight of young corn plants was recorded under Zn10Mn0 treatment due to Mn deficiency. Chlorophyll content decreased with high Zn application and this can be attributed to the interaction of Zn with iron in the growth medium. Different levels of Zn and Mn in nutrient solution did not have any significant effect on root parameters.

Phosphorus and Zinc Uptake and Their Interaction Effect on Dry Matter and Chlorophyll Content of Sweet Corn (Zea mays var. Saccharata)

Zinc and Phosphorus have antagonistic effect on the absorption and translocation of each other in plants. P-induced Zn deficiency is more common than Zn-induced P deficiency because growers commonly apply large amounts of P fertilizer as compared to Zn fertilizer. This research was conducted to examine the effect of different levels of Zn and P on the yield, Zn and P uptake and chlorophyll contents of corn plants. Sweet corn was grown in nutrient culture containing all combinations of Zn as ZnSO4.7H2O at levels of 0.0, 5.0, 10.0 and 20.0 mg L-1 and of P as KH2PO4 at levels of 0.0, 20.0, 40.0 and 80.0 mg L-1. Zn0P20 treatment produced the highest yield and the yields were decreased with P application in combination with Zn. The lowest dry weight of young corn plants was recorded under Zn0P80 treatment at both harvesting times due to both Zn deficiency and P toxicity. Chlorophyll content decreased with high Zn and P applications and this can be attributed to the interactions of Zn and P with iron in the growth medium. Zn0P80 treatment had the lowest Zn and the highest P uptake by shoot at 14 days after transplanting. The study has shown that Zn deficiency can enhance P uptake and translocation to such an extent that P may accumulate to toxic level in leaves. Zn20P80 treatment produced the highest Zn and P uptake by roots. Zn and P uptake by roots increased with increased Zn and P supply.

Quantification of Bacillus thuringiensis Cry1Ab protein in tissues of YieldGard ® (MON810) corn hybrids tested at multiple field locations in India

Transgenically expressed Bacillus thuringiensis insecticidal-protein Cry1Ab was quantified in target tissues of insect feeding of several YieldGard ® corn hybrids. The Cry1Ab protein is intended to protect corn plants from two economically important stem borers, Chilo partellus and Sesamia inferens. A total of seven YieldGard hybrids, all with MON810 event, were field-tested in a total of fourteen locations during the dry season (October–March) of 2005/2006 and wet season (May–October) of 2006. S. inferens and C. partellus oviposit on leaves of young corn plants, 15–60 days after emergence (DAE). The neonates initially feed by scraping the leaf lamina before migrating to bore into the stem. Thus high concentrations of Cry1Ab in whorl leaf and stem tissues would ensure effective control of the borers. The mean tissue Cry1Ab concentrations during the oviposition window of the borers (15–60 DAE), ranged from 50.05 to 21.01 ppm in whorl leaf, and between 9.26 and 3.47 ppm in stem tissue during the same period in the dry season of 2005/06. Similarly, Cry1Ab concentrations in whorl leaf and stem between 15 and 60 DAE during the wet season of 2006 ranged between 19.30 to 11.08 and 14.28 to 4.69 ppm, respectively. The baseline-sensitivity data of these insects to Cry1Ab in laboratory assays was determined. The concentrations of Cry1Ab in the target tissues as studied in seven YieldGard hybrids tested suggest effective management of the two borers. This paper also provides a summary of the expression of the C ry1Ab gene in various genetic backgrounds.

Corn Response to Fluid Fertilizers Placed Near the Seed at Planting

As corn producers strive to improve the efficiency of fertilizer use in corn (Zea mays L) production, placement of fertilizer near the seed is a management option that should be given serious consideration. The positive effect of fertilizer placed in a band close to corn seed when soil test values for P and/or K are lower than in the high range has been frequently documented in the literature. Placement of fertilizer very near the seed at planting, frequently referred to as “pop‐up” is gaining in popularity. Rate of adoption of this practice by crop producers has accelerated in recent years raising several questions. To address these questions, this study was conducted for the purpose of evaluating the impact of three fluid fertilizers applied at two rates and placed near the seed at planting on corn emergence, early growth, P uptake, and yield. All combinations of three factors (fertilizer grade, rate of application, placement) were combined in a complete factorial in fields of six cooperating farmers. Three fluid fertilizers were applied at two rates either with the seed or in positions above or below the seed with a small amount of soil between seed and fertilizer. Use of 10–15–0 (10–34–0) near the seed at 93.5 L ha−1 in sandy soils reduced emergence. In the same sandy soils, application of 4–4.4–8.3 (4–10–10) and 3–8‐15 (3–18–18) had no impact on emergence. Placement of all grades near the seed had no effect on emergence in the fine‐textured soils. The data lead to the conclusion that the rate of N, rather than the rate of N plus K, in the fertilizer to be placed near the seed should be the major consideration. Early growth and P uptake by young corn plants was improved by fertilizer placed close to the seed in fine‐textured soils; but not sandy soils. Five of six sites selected had high or very high levels of soil test P. Therefore, fertilizer placed near the seed did not have a positive effect on yield. Measured reductions in yield paralleled reductions in emergence. Results of the study show that placement of fertilizer near the corn seed at planting can be an effective management practice with minimal risk if soils are not sandy.

Impact of Banded Potassium on Crop Yield and Soil Potassium in Ridge‐Till Planting

Adequate application of fertilizer K has been identified as a key management practice needed to achieve optimum production in a ridge‐till planting system. However, the impact of K fertilization frequency has not been documented. Additionally, banded application of K also raises questions about the correct procedure to be followed for collection of soil samples. This study was conducted in the fields of three farmers who used the ridge‐till planting system for corn (Zea mays L.) and soybean (Glycine max L.) grown in rotation. Potassium was applied in a subsurface band in the center of existing ridges in the fall of Year 1 before corn and Year 2 before soybean at rates of 0, 18.5, 37.0, 55.5, and 74.0 kg ha−1 To measure the effect of residual K on soybean yield, the rates were doubled and applied only once (before Year 1). Grain yield of both corn and soybean at all sites was not affected by K application. Potassium uptake by young corn plants was increased by K rate, but uptake was not related to yield. Potassium use had no significant effect on K concentration in the most recently matured soybean trifoliate leaves sampled at early bloom. At two sites, banded K produced changes in soil test K to a depth of 15.0 cm at a distance to 15.0 cm from the row.

COMPARISON OF EXTRACTANTS USED FOR EVALUATING THE BIOAVAILABILITY OF SOIL P AND K

Numerous extractants including strong and weak acids and their salts, alkaline solutions, water etc. are used to evaluate the phosphorus and potassium status of soils. In our study, two weak extractants, hot water[1] and ammonium lactate[2] were used for the analyses. Hot water percolation (HWP) procedure developed in Hungary, seems to be a promising extraction methodology for rapid soil tests. The main objective of our study was to compare the results obtained with the two extraction procedures and to evaluate their use in estimating the bioavailability of soil P (Hw-P and AL-P mg kg−1) and K (Hw-K and AL-K mg kg−1) in different soil types. Soil samples were collected from experiments carried out with several NPK fertilizer sources applied in different treatment combinations. Four soil types (an Eutric cambisol in FAO taxonomy and Ortic Eutrochrept in USA taxonomy), a Haplic luvisol (FAO), Typic Hapludalf, a Stagnic Luvisol (FAO), Typic Endoaqualf and a Chromic Luvisol (FAO), Arenic Hapludalf, respectively, were used in the study. Main characteristics of experimental soils showed considerable differences. Results obtained with the two extractants were compared to each other as well as to amounts of P and K (Pup and Kup, respectively) removed by young corn and sunflower plants. Nutrient uptake of plants showed a dramatic increase compared to the control with the application of fertilizer sources not causing acid forming reactions in soils. From the results of statistical analyses, it was evident that a good correlation was found between the values of soil P and K obtained with the two extractants (“r” values ranged between 0.974 and 0.612 for P and between 0.761 and 0.04 for K, respectively). Generally, a better relationship could be observed between Hw-P and AL-P values than Hw-K and AL-K values. Similar tendencies were found when plant P and K removal was correlated with soil P and K contents extracted either with hot water or AL solution. Plant removal of P showed a better correlation with AL-extractable phosphorus. Among soils, closest relationships were observed between plant removal and soil P contents using the two extractants on the Orthic Eutrochrept (r=0.925 and 0.932, respectively). On the other hand, a better correlation was obtained between Hw-K values and K removal for the Typic Hapludalf as well as for the Arenic Hapludalf than between the soil P extracted by AL solution and P removal by young plants. For the wider understanding of dominant factors influencing the effectiveness of these extractants, especially for HWP, and their relationships with plant removal in a variety of soil types in Hungary, further studies are needed.

A non-Mendelian inheritance of resistance to strobilurin fungicides in Ustilago maydis.

Mutants of Ustilago maydis (DC) Corda with high resistance to azoxystrobin (RF 164 to 4714, based on EC50 values), an inhibitor of mitochondrial electron transport at the cytochrome bc1 complex, were isolated in a mutation frequency of 2.3 x 10(-7) after nitrosoguanidine mutagenesis and selection on media containing 1 microgram ml-1 azoxystrobin in addition to 0.5 mM salicylhydroxamate (SHAM), a specific inhibitor of cyanide-resistant (alternative) respiration. Oxygen uptake in whole cells was strongly inhibited in the wild-type strains by azoxystrobin (1.5 micrograms ml-1) in addition to SHAM (1 mM), but not in the mutant isolates. Genetic analysis with nine such mutant isolates resulted in progeny phenotypes which did not follow Mendelian segregation, but satisfied the criteria of non-Mendelian (cytoplasmic) heredity. In crosses between three mutant isolates with the compatible wild-type strains, the sensitivity was inherited by progeny maternally from the wild-type parent strain (criterion of uniparental inheritance). In crosses between wild-type strains and remaining mutant isolates, a continuous distribution of sensitivity in the progeny was found (criterion of vegetative segregation). The third criterion of cytoplasmic resistance (criterion of intracellular selection) was fulfilled by experiments on the stability of resistance phenotypes. With two exceptions, a reduction of resistance was observed in the mutant strains when they were grown on inhibitor-free medium. Recovery of the high resistance level was observed after they were returned to the selection medium. Cross-resistance studies with other fungicides, which also inhibit electron transport through complex III of respiratory chain, showed that mutations for resistance to azoxystrobin were also responsible for reduced sensitivity to kresoxim-methyl (RF 18 to 1199) and to antimycin-A (RF 20 to 305), which act at the Qo and Qi sites of the cytochrome bc1 complex, respectively. Studies of the fitness of azoxystrobin-resistant isolates showed that these mutations appeared to be pleiotropic, having significant adverse effects on growth in liquid culture and pathogenicity on young corn plants.

The effects of abiotic factors on induced volatile emissions in corn plants.

Many plants respond to herbivory by releasing a specific blend of volatiles that is attractive to natural enemies of the herbivores. In corn (Zea mays), this induced odor blend is mainly composed of terpenoids and indole. The induced signal varies with plant species and genotype, but little is known about the variation due to abiotic factors. Here, we tested the effect of soil humidity, air humidity, temperature, light, and fertilization rate on the emission of induced volatiles in young corn plants. Each factor was tested separately under constant conditions for the other factors. Plants released more when standing in dry soil than in wet soil, whereas for air humidity, the optimal release was found at around 60% relative humidity. Temperatures between 22 degrees C and 27 degrees C led to a higher emission than lower or higher temperatures. Light intensity had a dramatic effect. The emission of volatiles did not occur in the dark and increased steadily with an increase in the light intensity. An experiment with an unnatural light-dark cycle showed that the release was fully photophase dependent. Fertilization also had a strong positive effect; the emission of volatiles was minimal when plants were grown under low nutrition, even when results were corrected for plant biomass. Changes in all abiotic factors caused small but significant changes in the relative ratios among the different compounds (quality) in the induced odor blends, except for air humidity. Hence, climatic conditions and nutrient availability can be important factors in determining the intensity and variability in the release of induced plant volatiles.

Genetic Control of Resistance to the Piperidine Fungicide Piperalin in Ustilago maydis

Mutants of Ustilago maydis resistant to the piperidine fungicide piperalin were isolated in a mutation frequency of 2.4 x 10 - 5 after UV-irradiation and selection on media containing 50 μg ml - 1 piperalin. Genetic analysis with 15 such mutant isolates resulted in the identifications of two unlinked chromosomal loci, the U/ppl-1 locus with two allelic genes (U/ppl-1A and U/ppl-1B) and the U/ppl-2 locus. The U/ppl-2 and U/ppl-1A mutations are responsible for two levels of moderate and high resistance to piperalin (resistance factor, Rf: 54 and 135, respectively, based on effective concentration causing a 50% reduction in the growth rate, EC 5 0 ), while the U/ppl-1B mutation gives only a small reduction (approximately 8-fold) in piperalin sensitivity. Cross-resistance studies with other SBIs shows that the major gene (U/ppl-2 and U/ppl-1A) mutants are resistant to fenpropidin (Rf: 43 and 68), fenpropimorph (Rf: 261 and 283) and tridemorph (Rf: 9 and 10), but not to the inhibitors of C-14 demethylase (DMIs) and squalene epoxidase. The minor gene mutation U/ppl- I B codes a low-level of resistance (approximately 5-12-fold) to the above morpholine-type fungicides, but in contrast with the major gene mutations it increases 2-10 times the sensitivity to triazoles: triadimefon, triadimenol, propiconazole and flusilazole. Crosses between mutants carrying the U/ppl-genes with compatible isolates carrying the U/fpd, U/fpm or U/tdm mutations, which have been identified in previous genetic works for resistance to morpholine-type fungicides, yielded, with the exception of U/ppl-2 x U/fpm-2 cross, a large number of recombinants with wild-type sensitivity, indicating that the mutant genes involved in these crosses, were not allelic. An additive gene effect was observed only between nonallelic minor genes U/ppl-1B and U/fpm-1B or U/tdm-1,2. Studies of the fitness of piperalin-resistant isolates showed that the reduced sensitivity of major gene mutants was not associated with changes on the phytopathogenic fitness determining characteristics, such as growth in liquid culture and pathogenicity on young corn plants. Conversely, the minor gene mutation U/ppl-1B appeared to be pleiotropic, having significantly adverse effects on the phytopathogenic fitness.

Genetic Control of Resistance to the Piperidine Fungicide Fenpropidin in Ustilago maydis

Mutants of Ustilago maydis (DC.) Corda, resistant to the piperidine fungicide fenpropidin, were isolated in a mutation frequency of 3.2 × 10–5, after UV‐irradiation and selection on media containing 75 μg/ml fenpropidin. Genetic analysis with 15 such mutant isolates resulted in the identification of two unlinked chromosomal loci, U/fpd‐1 and U/fpd‐2. The U/fpd mutations are responsible for moderate resistance levels to fenpropidin (Rf: 42–56 or 15 based on effective concentration causing a 50% reduction in the growth rate (EC50) or minimal inhibitory concentration (MIC) values, respectively). Haploid strains carrying both U/fpd mutations do not exhibit higher levels of resistance to fenpropidin, indicating no additivity of gene effect between non‐allelic genes. Cross‐resistance studies with other Sterol Biosynthesis inhibitors (SBIs) showed that the U/fpd‐mutant isolates exhibited a positive cross‐resistance to the piperidine piperalin and to the related morpholine fungicides fenpropimorph and tridemorph, but not to the inhibitors of C‐14 demethylase and squalene epoxidase. Crosses between mutants carrying the U/fpd‐genes with compatible isolates carrying the U/fpm or U/tdm mutations, which have been identified in previous genetic studies for resistance to morpholine fungicides fenpropimorph and tridemorph, yielded, with the exception of U/fpd‐2 × U/fpm‐2 crosses, a large number of recombinants with wild‐type sensitivity, indicating that the mutant genes involved were not allelic. Analysis of progeny from crosses between U/fpd‐2 and U/fpm‐2 mutants yielded no recombinants with wild‐type sensitivity, but a 1 : 1 progeny segregation was observed at the MIC for the U/fpd‐2 isolates, indicating that these genes are alleles of the same locus. A study of the fitness of fenpropidin‐resistant isolates showed that the U/fpd mutations do not affect the phytopathogenic fitness‐determining characteristics such as growth in liquid culture and pathogenicity on young corn plants.

Genetic control of resistance to tridemorph inustilago maydis

Mutants ofUstilago maydis with low resistance to tridemorph isolated in a mutation frequency of 7x 10-6 after UV-irradiation and selection on media containing 25 μg ml-1 tridemorph. Genetic analysis with nine such mutant isolates resulted in the identification of two unlinked chromosomal loci,U/tdm- 1 andU/tdm- 2. TheU/tdm mutations are responsible for low resistance levels to tridemorph (resistance factor, Rf, of 3 or 5 based on effective concentration causing a 50% reduction in the growth rate (EC50) or minimal inhibitory concentration (MIC) values, respectively) and low to moderate level of resistance to fenpropimorph (Rf 10 or 16 based on MIC or EC50, respectively) and fenpropidin (Rf 5 or 11 based on MIC or EC50, respectively). Haploid strains carrying bothU/tdm mutations exhibit higher levels of resistance to the above fungicides, indicating interallelic interaction between nonallelic genes. Crosses between mutants carrying theU/tdm- genes with compatible isolates carrying theU/fpm- 1 orU/fpm- 2 mutations, which were found in previous work to carry fenpropimorph resistance, yielded in all cases a large number of recombinants with wild-type sensitivity, indicating that the mutant genes involved were not allelic. Cross-resistance studies with the inhibitors of C-14 demethylase showed that. the U/tdm-mutations were responsible for increased sensitivity to the triazoles triadimefon, triadimenol, propiconazole and flusilazole, and to the pyridine pyrifenox. Study of gene effect on the fitness ofU. maydis showed thatU/tdm-mutations appeared to be pleiotropic, having more or less adverse effects on growth rate in liquid culture and pathogenicity on young corn plants.