Asunción Morte

Effect of drought stress on growth and water relations of the mycorrhizal association Helianthemum almeriense-Terfezia claveryi

Abstract Plants of Helianthemum almeriense were micropropagated on MS medium and inoculated in vitro with Terfezia claveryi mycelium on MH medium and vermiculite. Mycorrhizal (M) and non-mycorrhizal (NM) plants were subjected to a drought stress period of 3 weeks in greenhouse conditions with the soil matric potential maintained at –0.5 MPa. Drought stress did not affect the amount of mycorrhizal colonization. The survival rate of M plants at the end of the drought stress period was higher than that of NM plants. The water potential was higher in M plants than in NM plants by 14% in well-watered and 26% in drought-stressed plants. Transpiration, stomatal conductance and net photosynthesis were higher in M plants than in NM plants. Transpiration was 92% higher in M plants than in NM plants under drought-stress conditions and 40% when irrigated. Stomatal conductance was 45% and 14% higher and net photosynthesis 88% and 54% higher, respectively, in M than in NM plants. Drought-stressed M plants accumulated more N, P and K than drought-stressed NM plants. Reduced negative effects of drought stress on H. almeriense by the desert truffle T. claveryi could be ascribed to specific physiological and nutritional mechanisms, suggesting that this mycorrhizal symbiosis aids adaptation to arid climates.

Variations in water status, gas exchange, and growth in Rosmarinus officinalis plants infected with Glomus deserticola under drought conditions

The influence of the arbuscular mycorrhizal fungus Glomus deserticola on the water relations, gas exchange parameters, and vegetative growth of Rosmarinus officinalis plants under water stress was studied. Plants were grown with and without the mycorrhizal fungus under glasshouse conditions and subjected to water stress by withholding irrigation water for 14 days. Along the experimental period, a significant effect of the fungus on the plant growth was observed, and under water stress, mycorrhizal plants showed an increase in aerial and root biomass compared to non-mycorrhizal plants. The decrease in the soil water potential generated a decrease in leaf water potential (psi(l)) and stem water potential (psi(x)) of mycorrhizal and non-mycorrhizal plants, with this decrease being lower in mycorrhizal water-stressed plants. Mycorrhization also had positive effects on the root hydraulic conductivity (Lp) of water stressed plants. Furthermore, mycorrhizal-stressed plants showed a more important decrease in osmotic potential at full turgor (psi(os)) than did non-mycorrhizal-stressed plants, indicating the capacity of osmotic adjustment. Mycorrhizal infection also improved photosynthetic activity (Pn) and stomatal conductance (g(s)) in plants under water stress compared to the non-mycorrhizal-stressed plants. A similar behaviour was observed in the photochemical efficiency of PSII (Fv/Fm) with this parameter being lower in non-mycorrhizal plants than in mycorrhizal plants under water stress conditions. In the same way, under water restriction, mycorrhizal plants showed higher values of chlorophyll content than did non-mycorrhizal plants. Thus, the results obtained indicated that the mycorrhizal symbiosis had a beneficial effect on the water status and growth of Rosmarinus officinalis plants under water-stress conditions.

Morphological characterization of the mycorrhiza formed by Helianthemum almeriense Pau with Terfezia claveryi Chatin and Picoa lefebvrei (Pat.) Maire

This work presents the first anatomical description of the mycorrhizal systems of Helianthemum almeriense, and of the structure and ultrastructure of the mycorrhizae formed by this plant species with the ascomycetes Terfezia claveryi and Picoa lefebvrei. Four different mycorrhizal systems are described, the club-shaped mycorrhiza being the most abundant. The type of mycorrhiza formed depended on the mycorrhiza culture conditions, but not on the fungal species. For both fungal species, H. almeriense formed an endomycorrhiza in natural field conditions, an ecto- and ectendomycorrhiza without a sheath in pot cultures, and an ectomycorrhiza with a characteristic sheath and Hartig net in in vitro cultures. This is the first report of a typical sheath in Helianthemum-desert truffle mycorrhizal associations. The results support the idea that culture conditions can induce changes in mycorrhiza morphology and that there is no clear barrier between the two main types of mycorrhiza organization in Helianthemum species. The ultrastructural study confirmed the regular presence of T. claveryi intracellular hyphae in direct contact with the host wall, a localization which seems to be a characteristic of the T. claveryi mycorrhiza organization. The P. lefebvrei mycorrhiza organization was characterized by intracellular hyphae with large amounts of electron-dense globules, probably with a lipidic content, and a warty ornamentation on the wall of the root external hyphae.

Growth and Water Relations in Mycorrhizal and Nonmycorrhizal Pinus Halepensis Plants in Response to Drought

Mycorrhizal and nonmycorrhizal Pinus halepensis plants were subjected to water stress by withholding irrigation for four months and then rehydrated for 30 d. Water stress affected plants growth and mycorrhizal association was unable to avoid the effects of drought on plant growth. However, when irrigation was re-established the increase in height, number of shoots, total dry mass, and chlorophyll content in the mycorrhizal plants were greater than in non-mycorrhizal plants. The decrease in soil water content decreased the leaf water potential, leaf pressure potential and stomatal conductance. These decreases were higher for nonmycorrhizal than for mycorrhizal plants, indicating that the mycorrhizal fungi permit a higher water uptake from the dry soils. The total content of inorganic solutes was not changed by presence of mycorrhizae.

Responses of tomato plants associated with the arbuscular mycorrhizal fungus Glomus clarum during drought and recovery

Mycorrhizal and non-mycorrhizal tomato plants ( Lycopersicon esculentum Mill. cv ‘Amalia’) were subjected to water stress by withholding irrigation water for 72 hours and then reirrigated for 120 hours. Water stress reduced root mycorrhizal colonization, although the presence of the fungus Glomus clarum stimulated tomato plant growth. During the stress period the effect on the growth was more pronounced in aerial biomass than in the root biomass. The decrease in the soil water potential generated a decrease in leaf water potential (Ψ l ) and leaf turgor potential (Ψ t ), particularly in the non-mycorrhizal plants. Although the absence of osmotic adjustment provoked the loss of turgor in stressed plants, both Ψ l and Ψ t recovered after a short reirrigation period. Mycorrhizal infection improved photosynthetic activity (P n ) and stomatal conductance (g s ) in non-stressed and stressed plants. These increases were accompanied by higher root hydraulic conductivity values, indicating enhanced water uptake in drought conditions. Neither P n nor g s fully recovered after rewatering. The beneficial effect of the mycorrhizal symbiosis on the water status of tomato plants stimulated plant growth.

Effects of high vineyard temperatures on the grapevine leafroll associated virus elimination from Vitis vinifera L. cv. Napoleon tissue cultures

Abstract In vitro culture of shoot tips and axillary buds was used for virus elimination from the Spanish autochthonous table grapevine cultivar Napoleon which was infected by Grapevine leafroll associated virus -3 (GLRaV-3) and Grapevine fanleaf virus (GFLV). High percentages of GLRaV-3-free plants (91–100%) were obtained by establishing shoot tip cultures from infected mother plants of the 29-228, 74-16 and 77-266 clones. Lower percentages of virus-free plants (71–87%) were obtained by in vitro culture of the first, the second and the third axillary buds of the growing distal shoots. Percentages of virus-free plants obtained with both shoot tips and axillary buds varied according to the time of the year when the explants were collected and the bud position on the shoot. A increased efficiency of in vitro tissue culture methods was observed when cultures were established in summer and it was due in part to the high vineyard temperatures reached in the southeast of Spain during the hot season. GFLV- and GLRaV-3-free plants were only obtained by thermotherapy in combination with tissue culture methods from co-infected plants of the clone 39-29.

Biotechnology and Cultivation of Desert Truffles

Among the ascomyces truffles, there are several genera with an excellent record as edible fungi, and two of these are of considerable economic importance: Terfezia and Tuber. Of these two genera, only Tuber had been cultivated commercially (for decades), until now. More recently, biotechnological methods on fungal inoculum and mycorrhizal plant production, as well as plantation management, have been developed to cultivate, for the first time, some species of the Terfezia genus (Honrubia et al. 2001, 2005; Morte et al. 2004, 2006). These procedures are presented in this chapter. Here, we attempt to evaluate conclusions on the basis of recent truffle production data from the first field plantations. The genus Terfezia belongs to the so-called “desert truffles” which are a complex family of mycorrhizal hypogeous fungi, mainly containing species of the genera Terfezia, Picoa, Tirmania and Tuber. Their geographical distribution is limited to arid and semiarid lands, mostly in countries around the Mediterranean basin, such as: southern Spain, Portugal, Italy, France, Hungary, Turkey, from Morocco to Egypt, Israel, the Arabian Peninsula, Iran, Iraq, Libya, Syria, and Kuwait. In addition, some desert truffle species have been found in South Africa (Botswana) (Marasas and Trappe 1973), in North America and Japan (Trappe and Sundberg 1977), and China (Wang, unpublished data). Generally, the regions where desert truffles grow have an annual rainfall which ranges from 50 to 380 mm. The truffle season produces good yields if the rainfall ranges from 70 to 120 mm in North African countries and from 100 to 350 mm in countries of southern Europe. The rainfall distribution is very important as far as both quantity and the time of the rainfall are concerned; that is, no later than the beginning of December in North African and Middle Eastern countries and no later than the beginning of October in countries of southern Europe.

Desert Truffle Cultivation in Semiarid Mediterranean Areas

This chapter focusses on showing some taxonomic and ecological characters of the main desert truffle species in Spain as well as the main biotechnological procedures followed to produce mycorrhizal plants with some of these fungal species. The full micropropagation protocol of the host plant Helianthemum violaceum is described for the first time. Five different ways of producing mycorrhizal synthesis between desert truffles and the Helianthemum species are reported, according to the type of fungal inoculum, plant source and culture conditions used. Finally, a management protocol for the established desert truffle plantations is discussed. Irrigation, one of the most important factors considered for successful cultivation, should be applied at the end of the summer during dry years when rainfall is less than 150 mm and for a second time at the beginning of the fruiting season in very dry years.

Alleviation of salt stress in citrus seedlings inoculated with arbuscular mycorrhizal fungi depends on the rootstock salt tolerance

Seedlings of Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and Alemow (Citrus macrophylla Wester) were inoculated with a mixture of AM fungi (Rhizophagus irregularis and Funneliformis mosseae) (+AM), or left non-inoculated (-AM). From forty-five days after fungal inoculation onwards, half of +AM or -AM plants were irrigated with nutrient solution containing 50 mM NaCl. Three months later, AM significantly increased plant growth in both Cleopatra mandarin and Alemow rootstocks. Plant growth was higher in salinized +AM plants than in non-salinized -AM plants, demonstrating that AM compensates the growth limitations imposed by salinity. Whereas AM-inoculated Cleopatra mandarin seedlings had a very good response under saline treatment, inoculation in Alemow did not alleviate the negative effect of salinity. The beneficial effect of mycorrhization is unrelated with protection against the uptake of Na or Cl and the effect of AM on these ions did not explain the different response of rootstocks. This response was related with the nutritional status since our findings confirm that AM fungi can alter host responses to salinity stress, improving more the P, K, Fe and Cu plant nutrition in Cleopatra mandarin than in Alemow plants. AM inoculation under saline treatments also increased root Mg concentration but it was higher in Cleopatra mandarin than in Alemow. This could explain why AM fungus did not completely recovered chlorophyll concentrations in Alemow and consequently it had lower photosynthesis rate than control plants. AM fungi play an essential role in citrus rootstock growth and biomass production although the intensity of this response depends on the rootstock salinity tolerance.

Expression Analysis of Aquaporins from Desert Truffle Mycorrhizal Symbiosis Reveals a Fine-Tuned Regulation Under Drought

We have performed the isolation, functional characterization, and expression analysis of aquaporins in roots and leaves of Helianthemum almeriense, in order to evaluate their roles in tolerance to water deficit. Five cDNAs, named HaPIP1;1, HaPIP1;2, HaPIP2;1, HaPIP2;2, and HaTIP1;1, were isolated from H. almeriense. A phylogenetic analysis of deduced proteins confirmed that they belong to the water channel proteins family. The HaPIP1;1, HaPIP2;1, and HaTIP1;1 genes encode functional water channel proteins, as indicated by expression assays in Saccharomyces cerevisiae, showing divergent roles in the transport of water, CO2, and NH3. The expression patterns of the genes isolated from H. almeriense and of a previously described gene from Terfezia claveryi (TcAQP1) were analyzed in mycorrhizal and nonmycorrhizal plants cultivated under well-watered or drought-stress conditions. Some of the studied aquaporins were subjected to fine-tuned expression only under drought-stress conditions. A beneficial effect on plant physiological parameters was observed in mycorrhizal plants with respect to nonmycorrhizal ones. Moreover, stress induced a change in the mycorrhizal type formed, which was more intracellular under drought stress. The combination of a high intracellular colonization, together with the fine-tuned expression of aquaporins could result in a morphophysiological adaptation of this symbiosis to drought conditions.