Plant Genetic Resources of Asparagus – Maintenance, Taxonomy and Availability
Globally germplasm collections contain more than 7.4 million accessions of plant genetic resources. Wheat represents the biggest group (856,168 accessions) followed by rice and barley but only 1,287 samples of 63 asparagus species are maintained. All the collections comprise wild and primitive forms, landraces as well as old and more recent cultivars of cultivated plants. The largest asparagus collections are in France (INRA) with 710 samples followed by USDA-ARS (USA) with 157 samples of 29 species (http://www.fao.org/wiews-archive/wiews.jsp). The German ex situ genebank is one of the ten largest global collections worldwide with 151,000 accessions. But only 33 asparagus accessions are available. In general, one of the big problems is the taxonomy of the samples. E.g., the French material is not determined. The genepool of asparagus is very well known but if the accessions are not taxonomically described the use for breeding is very difficult. And many of the species are not available in genebanks or only with a very few number of accessions. A gap analysis would be helpful in order to start collecting missions. Another topic is the availability. Due to international regulations like International Treaty of Plant Genetic Resources for Food and Agriculture (ITPGRFA) and Nagoya Protocol the access to material is getting more and more complicated. But nevertheless, screening of such collections shows a wide range of variability and gives the opportunity to find new breeding material.
Adaptation of Asparagus to Overwinter in Cold Climates
Asparagus is grown in a broad range of climates, varying not only for the levels of cold winter temperatures but also for the occurrence and severity of freezing events as plants enter or are released from dormancy. Consequently, cultivars bred in different regions can have distinct phenotypes for freezing tolerance and winterhardiness. Studies of hybrids with varying adaptation to the cold winter climate of Ontario, Canada have indicated the timing of fall acclimation and spring deacclimation and concentrations of certain cryoprotective compounds in the crown may be most important for survival. An improved understanding of winterhardiness can offering insights into breeding strategies and indirect selection criteria for the trait.
The Garden Asparagus (Asparagus officinalis L.) Genome Sequence Sheds Light on the Origin and Early Evolution of Sex Chromosomes
Garden asparagus (Asparagus officinalis L.) is dioecious species with a recently evolved homomorphic pair of X and Y sex chromosomes. Unlike mammalian X/Y sex chromosomes, recombination between the X and the Y is restricted to a small sex determination region and the Y-chromosome has not lost many genes relative to the X-chromosome. As a consequence, YY supermales are viable and indeed important in asparagus breeding systems. Sequencing and comparative analysis of YY male and XX female asparagus genomes has implicated a 1 Mb male-specific region on the asparagus Y chromosome. We have identified two independent male-to-hermaphrodite mutants that implicate a single gene in this male-specific region as responsible for dominantly interrupting pistil development. Anther development is not affected in these mutants but male-to-female conversions are seen in two other mutants with deletions spanning the 1 Mb non-recombining sex determination region. This region contains 12 gene models in addition to the female suppressor including a of a gene necessary for pollen development in the model plant system, Arabidopsis thaliana. The genome sequence of an XX female reveals a 150 Kb X-specific region that includes two X-specific protein-coding genes. These finding imply that the origin of a non-recombining sex determining region on the Asparagus proto-Y chromosome involved the linkage of a male promoting gene with a dominant suppressor of female organ development. The reference quality genomes that have been generated for garden asparagus and characterization of its sex determination system have implications for the future of asparagus breeding.
Asparagus decline and replant problem: A look back and a look forward at strategies for mitigating losses
Wade H. Elmer
Asparagus decline and the replant problem were both defined in the 1950s, but had been noted in asparagus fields long before. Although both conditions share many of the same features, there are distinct differences in the host symptoms and in the age of the field during the onset of symptoms. A number of factors contribute to both disorders. Abiotic factors, such as allelopathic residues, acidic soils, soil compaction, winter crown injury, and excessive harvest pressure, along with biotic agents like insects, weeds, and diseases contribute to decline and the replant problem. Toxic asparagus residues remain the major stressor in the replant problems. Although cultivar improvements along with close attention to reducing stress and disease outbreaks has lessened the damage from asparagus decline and the replant problem, these disorders still make serious inroads into field longevity and yield potential. The presentation will synthesize the results of numerous studies designed to enhance soil health and reduce asparagus decline and the replant problem. An assessment of the direction for future research projects will be presented.
Mechanization of white asparagus harvest – overview and perspectives
White asparagus is the most important vegetable crop in Germany. It is cultivated in ridges to keep the spears white and the tips closed. The spears are cut with long specific knifes, when the tips reach the top of the ridge. Hand harvest of white asparagus is very arduous, and labor and cost intensive. Since more than 60 years growers and manufacturers contemplate to facilitate this process.
In the beginning, asparagus was grown in ridges without any cover and had to be cut twice a day to keep the spears white. Only after using black films, it was possible to harvest once a day and the search became easier. The spears were cut and put into baskets, and then transported out of the field. In this time, more than four persons per ha were needed and the yield was low. The use of black/white films to cover the ridges changed the harvesting process dramatically. By turning the film from black to white, the temperature in the ridge can be regulated, which influences the growing velocity and, therefore, the daily yield. The many advantages of the film had one disadvantage. For harvesting, the film had to be taken down and put back afterwards. Different simplifications were carried out to accelerate the manual harvesting process. The employees had to learn how to dig free and to cut the spears in a minimum of time. Time measurements showed a variability to harvest one single spear between 2.5 and 18 s.
In parallel, different harvesting aids were developed. From single pulled one wheel carriages up to motor driven 5 rows harvesting aids different processes were tested to reduce harvesting costs. But the harvesting itself was still carried out by hand. Because of high machine costs and several logistic problems, these complicate harvesters were not successful. Today single row harvesting aids with electrical drive, which take the film up and put it later back are standard and harvesting with pulled carriages are the most used. Today less than one person is necessary to harvest one ha. In parallel, for many years different groups of growers and scientists tried to develop low cost mechanical white asparagus harvesters. Different detection, digging and cutting principles were tested but in the end the capacity per hour as well as the precision could not convince the growers. Additionally, the abrasion of the sandy soil caused a fast wear of the tools.
In the late 50th of the last century, a totally different development started to harvest asparagus for cans. The whole ridge was cut, taken and sieved by a moving sieve chain. Two to four employers sit at the end of the belt and sort the asparagus spears. This harvesting method was further developed in this century. Today the system is available on the market. The harvesting time and the amount of staff can be reduced distinctly in comparison to hand harvest. Additionally, loosen and sieving the ridge is very positive for asparagus quality. The disadvantages are the poor sorting – too many short spears -, harvesting periods longer than one week in bad weather periods and the high machine costs.
All in all, development of white asparagus harvesting is not completed. Most growers are still waiting for a selective white asparagus harvesting robot – fast, inexpensive and gentle to the produce – to reduce the high number of employers in the vegetable companies.