Crop-Specific Responses to Cold Stress and Priming: Insights from Chlorophyll Fluorescence and Spectral Reflectance Analysis in Maize and Soybean.

This study aimed to investigate the impact of cold stress and priming on photosynthesis in the early development of maize and soybean, crops with diverse photosynthetic pathways. The main objectives were to determine the effect of cold stress on chlorophyll a fluorescence parameters and spectral reflectance indices, to determine the effect of cold stress priming and possible stress memory and to determine the relationship between different parameters used in determining the stress response. Fourteen maize inbred lines and twelve soybean cultivars were subjected to control, cold stress, and priming followed by cold stress in a walk-in growth chamber. Measurements were conducted using a portable fluorometer and a handheld reflectance instrument. Cold stress induced an overall downregulation of PSII-related specific energy fluxes and efficiencies, the inactivation of RCs resulting in higher energy dissipation, and electron transport chain impairment in both crops. Spectral reflectance indices suggested cold stress resulted in pigment differences between crops. The effect of priming was more pronounced in maize than in soybean with mostly a cumulatively negative effect. However, priming stabilized the electron trapping efficiency and upregulated the electron transfer system in maize, indicating an adaptive response. Overall, this comprehensive analysis provides insights into the complex physiological responses of maize and soybean to cold stress, emphasizing the need for further genotype-specific cold stress response and priming effect research.

First Report of Hemp Fusarium Wilt Caused by Fusarium oxysporum in Croatia.

Wilted hemp (Cannabis sativa L.) plants were observed in August 2019 in commercial fields around Osijek, Croatia. Plants and roots with disease symptoms were collected. The single-spored isolates produced septate cottony white to light pink aerial mycelium and purple undersurface on potato dextrose agar (PDA). Smooth and hyaline hyphae were branched and septate. Macroconidia were fusiform to sickle-shaped with foot-shaped basal cells, elongated apical cells and three to five septa. Sequencing of the internal transcribed spacer and the partial elongation factor 1-α gene identified the species as Fusarium oxysporum. Artificial infection fulfills Koch's postulates, producing plants which show stunted growth and wilt symptoms similar to those observed in the commercial fields. Control seedlings remained symptomless and healthy. To the best of our knowledge, this is the first report of hemp Fusarium wilt causing F. oxysporum in Croatia. Considering that F. oxysporum has been reported in main field crops in Croatia, the presence of this pathogen could cause economically significant hemp production decreases, especially in humid and cold springs and susceptible varieties.

First Report of Charcoal Rot Caused by Macrophomina phaseolina on Hemp in Croatia.

The production of industrial hemp (Cannabis sativa) has had a sharp increase in the past five years in Croatia (Mihelcic 2017). Production has been in constant increase, from 1560 ha in 2015 to 2476 ha in 2019 (PAAFRD). In August 2019, numerous (~1.5%) premature wilted hemp plants (cultivar Fibranova) were observed in commercial fields in Vladislavci (45.4646950° N, 18.5674770° E), around Osijek, Croatia. Diseased plants showed symptoms of chlorosis, rapidly wilting, necrosis and prematurely dying. The stalk of diseased plants was completely desiccated, while internal tissues were spongy and fluffy. Near the soil line, discoloration of the stalk with small spherical to oblong black microsclerotia was detected. Roots were necrotic with brown-gray areas. Twenty root and crown segments of the infected plants (2- to 3-mm long pieces) were surface sterilized with 2% NaOCl for 5 min, rinsed three times with sterile distilled water, and plated on potato dextrose agar (PDA, pH 6.2) media, containing 250 mg per liter of chloramphenicol to inhibit bacterial growth (Zveibil and Freeman 2005). The culture plates were incubated at 28 ± 2°C for 7 days in the dark and purified to obtain a pure culture that produces numerous, dark, hard, ovoidal-shaped sclerotia, averaging 140 x 52 µm (n=50). The single sclerotium isolate produced flat light to dark gray colonies with entire margins. Based on field symptoms, colony and microsclerotia morphology, the fungus was identified as Macrophomina phaseolina (Tassi) Goid (Marquez et al. 2021). Total DNA from the isolate was extracted with Extract-N-Amp Plant PCR Kit (Sigma-Aldrich Co., USA). To confirm morphological identification, part of the TEF 1-alpha gene region was amplified using EF1-728F (Carbone and Kohn 1999) and EF2 (O'Donell et al. 1998). The sequence of the isolate MP1 (212 bp - GenBank accession no. OQ389757), showed 100% nucleotide sequence identity to the reference sequence of M. phaseolina GenBank sequence MG434668 (Casano et al. 2018). Eighteen hemp plants (cv. Fibranova) were sown in six plastic pots (three hemp plants per pot) for the pathogenicity test. Ten-day-old M. phaseolina culture (isolate MP1) was used for inoculum preparation. Each pot of one-week-old plant was irrigated with 100 ml of a microsclerotia suspension (105 microsclerotia/ml)(Abied et al. 2018). Plants were held at 28°C and 70% relative humidity in a growth chamber (aralab, Fitoclima 10.000 HP) with a 16-hour photoperiod. Pots with control plants were irrigated with the same amount of sterile distilled water. Ten weeks after inoculation percentage of wilted plants was 77.78%. In the control variant all plants were healthy. M. phaseolina was reisolated from inoculated plants and morphologically identified. With the liberalization of the law, hemp production in Croatia is increasing, which could result in general disease problems and the disease caused by M. phaseolina. Charcoal rot will be expressed in years with dry and warm summers (Lodha and Mawar 2020), and relatively short, cool, rainy winters (Nevo et al. 2012), which has become common in the last decade in Croatia. To our knowledge, this is the first report of M. phaseolina on hemp in Croatia. The authors declare no conflict of interest.

Genetic Diversity and Population Structure of European Soybean Germplasm Revealed by Single Nucleotide Polymorphism.

Soybean is the most grown high-protein crop in the world. Despite the rapid increase of acreage and production volume, European soybean production accounts for only 34% of its consumption in Europe. This study aims to support the optimal exploitation of genetic resources by European breeding programs by investigating the genetic diversity and the genetic structure of 207 European cultivars or American introductions registered in Europe, which were genotyped by the SoySNP50K array. The expected heterozygosity (He) was 0.34 for the entire collection and ranged among countries from 0.24 for Swiss cultivars to 0.32 for American cultivars (partly reflecting differences in sample size between countries). Cluster analysis grouped all genotypes into two main clusters with eight subgroups that corresponded to the country of origin of cultivars and their maturity group. Pairwise Fst values between countries of origin showed the highest differentiation of Swiss cultivars from the rest of the European gene pool, while the lowest mean differentiation was found between American introductions and all other European countries. On the other hand, Fst values between maturity groups were much lower compared to those observed between countries. In analysis of molecular variance, the total genetic variation was partitioned either by country of origin or by maturity group, explaining 9.1% and 3.5% of the total genetic variance, respectively. On the whole, our results suggest that the European soybean gene pool still has sufficient diversity due to the different historical breeding practices in western and eastern countries and the relatively short period of breeding in Europe.

The Combination of Increased Temperatures and High Irradiation Causes Changes in Photosynthetic Efficiency.

Global warming and the associated climate change are imposing abiotic stress on plants. Abiotic factors are crucial for plant productivity, survival, and reproduction. Eight sunflower hybrids were tested in conditions of different water availability and with combinations of different temperatures and irradiation. The changes in the photosynthetic efficiency were measured in the morning (control conditions: 2013, 25.8 °C and 349.1 W m-2; 2014, 21.8 °C and 296.4 W m-2) and afternoon (the combination of increased temperatures and high irradiation: 2013, 34 °C and 837.9 W m-2; 2014, 29.4 °C and 888.9 W m-2) at a flowering stage in rainfed or irrigated conditions. The measurement time (morning and afternoon conditions) had a statistically significant effect on all the tested parameters. The performance index (PIABS) in 2013 and the maximum quantum yield of photosystem II (TR0/ABS) in 2014 are the only parameters significantly affected by the irrigation. As a result of the combined effect of increased temperatures and high irradiation, PIABS values decreased by 73-92% in rainfed conditions and by 63-87% in irrigated conditions in 2013, depending on the hybrid, while in 2014, the decrease varied between 70 and 86%. The TR0/ABS decrease was 7-17% in 2013, depending on the hybrid, and 6-12% in 2014, both in rainfed and irrigated conditions. The principal component analysis confirmed the effect of the combination of increased temperatures and high irradiation on hybrids, sorting them exclusively according to the time of measurement. All investigated parameters highly fluctuated between hybrids but without observable trends for the morning and afternoon conditions, as well as for irrigation. Plants' reaction to the combination of increased temperatures and high irradiation manifested as a change in their photosynthetic efficiency, i.e., the photosynthetic apparatus' functioning was impaired.

Identification of mega-environments in Europe and effect of allelic variation at maturity E loci on adaptation of European soybean.

Soybean cultivation holds great potential for a sustainable agriculture in Europe, but adaptation remains a central issue. In this large mega-environment (MEV) study, 75 European cultivars from five early maturity groups (MGs 000-II) were evaluated for maturity-related traits at 22 locations in 10 countries across Europe. Clustering of the locations based on phenotypic similarity revealed six MEVs in latitudinal direction and suggested several more. Analysis of maturity identified several groups of cultivars with phenotypic similarity that are optimally adapted to the different growing regions in Europe. We identified several haplotypes for the allelic variants at the E1, E2, E3 and E4 genes, with each E haplotype comprising cultivars from different MGs. Cultivars with the same E haplotype can exhibit different flowering and maturity characteristics, suggesting that the genetic control of these traits is more complex and that adaptation involves additional genetic pathways, for example temperature requirement. Taken together, our study allowed the first unified assessment of soybean-growing regions in Europe and illustrates the strong effect of photoperiod on soybean adaptation and MEV classification, as well as the effects of the E maturity loci for soybean adaptation in Europe.