Amnon Bustan

Role of carbohydrate reserves in yield production of intensively cultivated oil olive (Olea europaea L.) trees

Olive (Olea europaea) has a very high tendency for year-to-year deviation in yield (alternate bearing), which has a negative economic impact on the olive oil industry. Among possible reasons for alternate bearing, depletion of stored carbohydrates (CHO) during the On-year (high yield) has often been mentioned. The objective of the present study was to verify the role of CHO reserves, as a cause or effect, in the alternate bearing of intensively cultivated olives. A monthly survey of soluble sugar and starch concentrations in the leaves, branches, bark and roots of On- and Off-trees (cv. Barnea) was carried out during a complete reproductive cycle from November 2005 to October 2006. Carbohydrate concentration in the sapwood was determined in January, as well as an estimate of whole-tree biomass. The trunk and limbs possess the largest portion of CHO reserves. The influence of reduced fruit load on CHO reserves was also investigated. Starch, mannitol and sucrose concentrations increased from December to March in all tissues, and then declined along with fruit development. Leaves, branches and bark have a significant role in CHO storage, whereas roots accumulated the lowest CHO concentrations. However, fluctuations in reserve content suggested considerable involvement of roots in the CHO budget. Nevertheless, there were no meaningful differences in the annual pattern of CHO concentration between On- and Off-trees. Even a 75-100% reduction in fruit number brought about only a minor, sluggish increase in CHO content, though this was more pronounced in the roots. Carbohydrate reserves were not depleted, even under maximum demands for fruit and oil production. It is concluded that in olives, the status of CHO reserves is not a yield determinant. However, they may play a significant role in the olives survival strategy, ensuring tree recovery in the unpredictable semiarid Mediterranean environment. This suggests that CHO reserves in olive act like an active sink, challenging the common concept regarding the regulation of CHO reserves in plants.

Fruit thinning using NAA shows potential for reducing biennial bearing of Barnea and Picual oil olive trees

Biennial bearing is a major horticultural and economic drawback of olive (Olea europaea L.) cultivation, which particularly affects the olive oil industry under intensive production systems. The number of fruits per tree in an on-year is a primary determinant of the biennial cycle. While fruit thinning using NAA shortly after full bloom is commonly practiced to increase fruit size in table olives, the extent of its influence on biennial bearing is unknown. In the present study, the ability of that common naphthaleneacetic acid (NAA) treatment (100 mg/L, 10 days after full bloom) to alleviate biennial bearing in two oil olive cultivars, Picual and Barnea, was poor, although significant influence on the number of fruit was evident solely in Barnea. Picual seemed less susceptible than Barnea to biennial bearing. Consequently, the effect of a broad range of NAA concentrations (0–320 mg/L, 10 days after full bloom) on various yield parameters was investigated during a biennial cycle of Barnea trees. There was a gradual proportional decline in the on-year number of fruits from ~50 000 to 10 000/tree in response to increasing NAA concentrations. The number of return fruits in the off-year was reciprocal to the on-year fruit load, but remained relatively small, below 15 000/tree. The dynamic relationship between fruit load and fruit size in both on- and off-years was a significant compensation factor in fruit and oil yields. In both cultivars, an on-year fruit load smaller than 20 000/tree is likely to provide consistent yearly oil yields ranging from 10 to 12 kg/tree. The results demonstrate the possibility of using NAA post-bloom spraying to balance biennial bearing in oil olives.

Introduced Tuber aestivum replacing introduced Tuber melanosporum: a case study

A Tuber melanosporum plantation established in 1994/1995 on Kibbutz Bar’am (in the Upper Galilee, Israel) gradually lost its T. melanosporum mycorrhiza. In 1999, T. aestivum inoculated seedlings were inadvertently introduced into the plantation to fill the gaps between trees. A single T. melanosporum fruit body was found in 1999. Although no truffles were found after 1999 and until 2009, in that year and in 2010, truffles were collected. Morphological and molecular analyses proved these to be T. aestivum. Thus, the intentionally introduced T. melanosporum mycorrhiza was replaced by that of another introduced mycorrhizal fungus, T. aestivum. Local oak species produced higher yields compared to introduced host species known to be good T. melanosporum plant symbionts. The yield was comparable to that reported for young commercial orchards, but the fruiting season was earlier than in Europe.

Analysis of phenotypic and genetic polymorphism among accessions of saltgrass (Distichlis spicata)

Morphological and genetic analyses were applied on 37 saltgrass (Distichlis spicata) accessions collected from distant locations throughout the American continent in order to: 1) develop and identify morphologic and genetic profiles for the saltgrass genotypes; 2) characterize the genetic distance among saltgrass accessions within the given germplasm collection; and 3) identify a possible linkage between patterns of genetic and eco-geographical parameters. Analysis based on 70 RAPD markers revealed broad polymorphism among the genotypes and enabled their individual characterization. A UPGMA dendrogram clustered the genotypes into groups according to a general pattern of their geographical origin. Yet, only the group of Californian accessions was significantly distinct from other groups, as determined by χ2 tests. Various statistical analyses indicated that only minor genetic differences existed between seashore and desert saltgrass genotypes, supporting that these two eco-geographical types belong to the same species, Distichlis spicata. Our results suggest that genetic interactions exist between geographically distant saltgrass populations, in spite of the dominance of clonal reproduction in this species. The contribution of dioecy, seed production, and epizoochory to the distribution patterns of saltgrass is discussed at the geographic and at the genetic levels.

Fruit load governs transpiration of olive trees

We tested the hypothesis that whole-tree water consumption of olives (Olea europaea L.) is fruit load-dependent and investigated the driving physiological mechanisms. Fruit load was manipulated in mature olives grown in weighing-drainage lysimeters. Fruit was thinned or entirely removed from trees at three separate stages of growth: early, mid and late in the season. Tree-scale transpiration, calculated from lysimeter water balance, was found to be a function of fruit load, canopy size and weather conditions. Fruit removal caused an immediate decline in water consumption, measured as whole-plant transpiration normalized to tree size, which persisted until the end of the season. The later the execution of fruit removal, the greater was the response. The amount of water transpired by a fruit-loaded tree was found to be roughly 30% greater than that of an equivalent low- or nonyielding tree. The tree-scale response to fruit was reflected in stem water potential but was not mirrored in leaf-scale physiological measurements of stomatal conductance or photosynthesis. Trees with low or no fruit load had higher vegetative growth rates. However, no significant difference was observed in the overall aboveground dry biomass among groups, when fruit was included. This case, where carbon sources and sinks were both not limiting, suggests that the role of fruit on water consumption involves signaling and alterations in hydraulic properties of vascular tissues and tree organs.

Mycorrhized Ri-transformed roots facilitate in vitro inoculation of Cistus incanus with Tuber melanosporum

Progress was made towards a reliable in vitro system for mycorrhizing Cistus incanus seedlings with Tuber melanosporum. A rich growth medium favored extensive growth of mycorrhized Ri-transformed roots (MTR) but inhibited mycelial outgrowth into the medium. A minimal medium, on the other hand, inhibited MTR growth but supported considerable mycelial outgrowth into the medium. While the presence of a C.␣incanus propagule clearly enhanced mycelial growth into the minimal medium, a highly significant factor appeared to be the use of MTR inoculant, which supported mycorrhizal development to the Hartig net stage. The advantages of MTR for in vitro mycorrhization of host plant seedlings are discussed.

Optimized conditions for mycorrhiza formation between the pink rockrose (Cistus incanus) and the black Périgord truffle ( Tuber melanosporum)

Motivated by the increasing interest in the black Perigord truffle (Tuber melanosporum), we have been seeking to develop a controlled cultivation method for this celebrated fungus. Our strategy is based on establishing optimal conditions for mycorrhizal development in detached media by mimicking natural productive truffle beds. Cistus incanus, a Mediterranean shrub, was used as host. The components of the growth medium—polystyrene foam flakes, Perlite, peat, and dolomite powder—provided the coarse and fine porosity required for adequate drainage, appropriate balance between aeration and moisture, the desired pH (7.5-8.2), and support of mycorrhizal development. Optimum rhizosphere temperatures for inoculation and continued mycorrhizal development were 20-25 °C. Inoculation with mycorrhized root fragments proceeded more rapidly than traditional inoculation with a carpophore suspension, particularly at suboptimal growth medium temperatures. A keystone of our system is to determine the optimum root volume re...

Salt-avoidance mechanisms in the halophyte Distichlis spicata as a promising source for improved salt resistance in crop plants

Salinity is an escalating problem in agriculture worldwide (Szabolics, 1989; Hamdy, 1996; Choukr-Allah, 1996). The use of recycled and saline waters to replace fresh water in agriculture contributes, among other factors, to the aggravation of salinity problems. Most crop plants are sensitive to salinity and poorly equipped to cope with salt stress without suffering from impaired growth and development, and even injury (Lauchli and Epstein, 1990; Maas, 1990). The adverse effects of salinity cause considerable reduction in yields, far below the economic threshold of most crops in present use. It can be stated quite confidently that the prevalent future environment of agricultural crops will be much more saline than today. Therefore, improving salt resistance of crop plants is of major interest in agricultural research. Halophytes are the ultimate candidates to serve as a genetic source for this purpose.

The use of saltgrass (Distichlis spicata) as a pioneer forage crop in salty environments

Almost 1 billion hectares of land in the world is affected by salinity and over 50% of irrigated lands have salinity problems (Flowers and Yeo, 1995). Salinization has been identified as a major process leading to desertification of agricultural lands. The process of salinization of arable lands is mostly (but not solely) caused by human activities, and it is associated with malpractices in irrigation projects, mostly in arid and semiarid countries. Soil salinization can also result from natural processes, such as inland intrusion of seawater (i.e. coastal areas of West Africa and northeast China) or due to continuous evaporation from shallow aquifers in desert environments (i.e. coastal regions of north Africa and the Pampas del Tamarugal in Chile).