This review deals with two essential plant mineral nutrients, iron (Fe) and phosphorus (P); the acquisition of both has important environmental and economic implications. Both elements are abundant in soils but are scarcely available to plants. To prevent deficiency, dicot plants develop physiological and morphological responses in their roots to specifically acquire Fe or P. Hormones and signalling substances, like ethylene, auxin and nitric oxide (NO), are involved in the activation of nutrient-deficiency responses. The existence of common inducers suggests that they must act in conjunction with nutrient-specific signals in order to develop nutrient-specific deficiency responses. There is evidence suggesting that P- or Fe-related phloem signals could interact with ethylene and NO to confer specificity to the responses to Fe- or P-deficiency, avoiding their induction when ethylene and NO increase due to other nutrient deficiency or stress. The mechanisms responsible for such interaction are not clearly determined, and thus, the regulatory networks that allow or prevent cross talk between P and Fe deficiency responses remain obscure. Here, fragmented information is drawn together to provide a clearer overview of the mechanisms and molecular players involved in the regulation of the responses to Fe or P deficiency and their interactions.

Yellow (stripe) rust, caused by the biotrophic fungus Puccinia striiformis f. sp. tritici (Pst), stands as the most serious wheat disease worldwide, affecting approximately 88% of world wheat production. Even though yellow rust generally develops in cool humid weather conditions, the expansion of new races adapted to warmer climates threatens zones where severe P. striiformis epidemics were infrequent, such as Andalusian wheat cropping areas. In order to characterize yellow rust resistance mechanisms in Spanish germplasm, our study evaluated 19 Spanish bread wheat cultivars against P. striiformis under controlled conditions for percentage of disease severity (DS) and infection type (IT). From this visual evaluation, 74% of evaluated cultivars showed resistant responses against P. striiformis infection with only five cultivars considered susceptible. Subsequently, macroscopic and microscopic components of resistance were identified through image analysis and histological studies, respectively, in six selected cultivars. Macroscopic parameters such as total pustule area and total affected area (%), together with microscopic parameters such as early-aborted and established microcolonies regarding plant cell death responses (%), and microcolony length (µm), were identified as capable of differentiating cultivars quantitatively. Thus, these parameters could be used as a basis for screening resistant responses in future breeding programs, complementary to physiology, genetic and biochemical studies of plant-Pst interaction. Finally, our study seems to be the first macroscopic and microscopic characterization of P. striiformis infection in a collection of Spanish bread wheat cultivars in controlled conditions.

Durum wheat cultivation in Mediterranean regions is threatened by abiotic factors, mainly related to the effects of climate change, and biotic factors such as the leaf rust disease. This situation requires an in-depth knowledge of how predicted elevated temperatures and [CO₂] will affect durum wheat-leaf rust interactions. Therefore, we have characterised the response of one susceptible and two resistant durum wheat accessions against leaf rust under different environments in greenhouse assays, simulating the predicted conditions of elevated temperature and [CO₂] in the far future period of 2070–2099 for the wheat growing region of Cordoba, Spain. Interestingly, high temperature alone or in combination with high [CO₂] did not alter the external appearance of the rust lesions. However, through macro and microscopic evaluation, we found some host physiological and molecular responses to infection that would quantitatively reduce not only pustule formation and subsequent infection cycles of this pathogen, but also the host photosynthetic area under these predicted weather conditions, mainly expressed in the susceptible accession. Moreover, our results suggest that durum wheat responses to infection are mainly driven by temperature, being considered the most hampering abiotic stress. In contrast, leaf rust infection was greatly reduced when these weather conditions were also conducted during the inoculation process, resembling the effects of possible heat waves not only in disease development, but also in fungal germination and penetration success. Considering this lack of knowledge in plant-pathogen interactions combined with abiotic stresses, the present study is, to the best of our knowledge, the first to include the effects of the expected diurnal variation of maximum temperature and continuous elevated [CO₂] in the durum wheat-leaf rust pathosystem.

Wheat interactions against fungal pathogens, such as Zymoseptoria tritici, are affected by changes in abiotic factors resulting from global climate change. This situation demands in-depth knowledge of how predicted increases in temperature and CO₂ concentration ([CO₂]) will affect wheat—Z. tritici interactions, especially in durum wheat, which is mainly grown in areas considered to be hotspots of climate change. Therefore, we characterized the response of one susceptible and two resistant durum wheat accessions against Z. tritici under different environments in greenhouse assays, simulating the predicted conditions of elevated temperature and [CO₂] in the far future period of 2070–2099 for the wheat-growing region of Córdoba, Spain. The exposure of the wheat—Z. tritici pathosystem to elevated temperature reduced disease incidence compared with the baseline weather conditions, mainly affecting pathogen virulence, especially at the stages of host penetration and pycnidia formation and maturation. Interestingly, simultaneous exposure to elevated temperature and [CO₂] slightly increased Z. tritici leaf tissue colonization compared with elevated temperature weather conditions, although this fungal growth did not occur in comparison with baseline conditions, suggesting that temperature was the main abiotic factor modulating the response of this pathosystem, in which elevated [CO₂] slightly favored fungal development.

Agropyron cristatum (P genome) is a Triticeae species from the wheat tertiary gene pool which has economic importance as forage and also displays traits beneficial to wheat. Resistance to leaf rust was previously mapped to the short arm of chromosome 1P (1PS) in A. cristatum by the development of a compensating Robertsonian translocation involving chromosome arm 1PS and the long arm of wheat chromosome 1B (1BL). In this study, chromosome arm 1PS was engineered using the ph1b mutation to induce 1BS/1PS homoeologous recombination and to obtain new translocations with shortened fragments of chromosome arm 1PS. Two translocations with different alien fragment sizes were identified by genomic in situ hybridization, wheat 1BS- and 1PS-specific molecular markers and gene-specific markers for glutenin, Glu-B3 and gliadin Gli-B1 seed storage protein. One translocation (called type 1) replaces a proximal segment of 1PS chromatin, and the other (called type 2) replaces a distal 1PS segment and introduces the Glu-B3 and Gli-B1 wheat storage protein loci. Six specific EST-STS markers for chromosome arm 1PS amplified PCR products in the recombinant type 2 translocation line. Resistance analysis showed that the type 2 translocation was highly resistant to a virulent race of leaf rust pathogen. The new wheat–A. cristatum translocations obtained yield material with seedling plant resistance to leaf rust and seed storage protein loci.