Cuadro 1. Rendimiento acumulado de diferentes cultivares de espárrago en cinco temporadas de cosecha (2001-2005).
Agricultura Técnica (Chile) 67(3):227-235 (Julio-Septiembre)
INVESTIGACIÓN PRODUCCIÓN VEGETAL
Evaluation of Green Asparagus Varietis in the Bio-Bio Region, Chile
Evaluación de Variedades de Espárrago Verde en la Región del Bío-Bío, Chile
María Inés González A.1
1 Instituto de Investigaciones Agropecuarias, Centro Regional de Investigación Quilamapu, Casilla 426, Chillán, Chile. E-mail: mgonzale@inia.cl ]]> Recibido: 30 de julio de 2006. Aceptado: 16 de octubre de 2006.
ABSTRACT
A trial was established using three month old asparagus (Asparagus officinalis L.) plants in a volcanic soil at Chillán (36°32’ S; 71°55’ W). Experimental design was randomized complete blocks with four replicates. Plots had four 6m long rows of plants. Distance between rows was 1.5 m and in-row 0.2 m. The evaluated cultivars were: ‘Atlas’, ‘Grande’ and ‘Apollo’ from Asparagus Seeds and Transplants (California), ‘Jersey Giant’, ‘Jersey Gem’, ‘Jersey General’, ‘Jersey King’, ‘Jersey Knight’ and ‘Jersey Supreme’ from Jersey Asparagus Farms (New Jersey), and the controls were ‘UC-157’ F1 and F2. Spears were trimmed 18 cm long after harvest. The highest cumulative marketable yield was obtained by ‘Jersey Supreme’ (43 Mg ha-1 in five years), and the lowest one by ‘Apollo’ (17.8 Mg ha-1). Marketable yield of both control ‘UC-157’ F1 (24.9 Mg ha-1) and F2 (24.3 Mg ha-1) was similar (P ≤ 0.05) to the other Jersey cultivars, but higher than ‘Apollo’. The main disadvantage of ‘Jersey Supreme’ is the purple coloration of its bud scales, and a purple cast to the butt of the spear, therefore discarded for the fresh market, but suitable for freezing. Another disadvantage is that spears tend to open to a smaller height than ‘UC-157’, and 10% more of its production is destined to internal market (País category).
Key words: Asparagus officinalis, cultivar, number of spears, quality, yield.
RESUMEN
Se estableció un ensayo con plantas de espárrago (Asparagus officinalis L.) de tres meses de edad, en un suelo derivado de cenizas volcánicas en Chillán (36°32’ lat. Sur; 71°55’ long. Oeste). El diseño experimental fue de bloques completos al azar con cuatro repeticiones. Las parcelas estuvieron compuestas por cuatro hileras de 6 m de largo. La distancia entre hileras fue de 1,5 m, y 0,2 m sobrePalabras clave: Asparagus officinalis, cultivar, número de turiones, calidad, rendimiento.
INTRODUCTION
The selection of asparagus (Asparagus officinalis L.) cultivars is important because plantations must remain productive for several years to recover the initial investment and obtain good returns. The productive response of a variety depends on the interaction between its genotype and the environment. Therefore, the cultivars must be evaluated in the zone where they will be introduced.
It is estimated that 90% of the surface with asparagus in Chile is planted with the ‘UC-157 F1’ and ‘UC-157 F2’ varieties as the seed of the F2 generation is produced in the country and the quality of the commercial product has been good, with a tight spear and deep green color. However, the fact that this production is based practically on one variety only is a risk from the sanitary point of view. The yields of asparagus in Chile have been decreasing during the last few years, sometimes down to levels that make cultivation barely profitable; this situation may be due to the variety cultivated and/or mistakes in the management of the plantations.
‘UC-157’ is one of the most planted green asparagus cultivar on the warm and temperate zones of the world. Many trials have been conducted in different places to find new alternatives of asparagus cultivars using ‘UC-157’ as control (Carballo et al., 1992; McCormick and Thomsen, 1995; Mullen et al., 1996; Cueto and Lesnick, 1999; Garrison et al., 1999; Mullen et al., 1999; Stone and Roose, 1999; Drost, 2002; Mullen et al., 2002), plus the International Asparagus Cultivar Trials (IACT) organized by the Asparagus Working Group of the International Society for Horticultural Science (Knaflewski, 1996; Paschold et al., 1996; Van Oordt et al., 1999; Benson, 2002; Jinsong, 2002). In general, ‘UC-157’ yield is very low in cold climates localities in Europe, where the German and Dutch cultivars predominate (Knaflewski, 1996b; Paschold et al., 1996). ]]>
Asparagus cultivar evaluation trials have been conducted in different zones of Chile from the beginnings of the 90 decade, with the objective to find new cultivars that could replace or complement ‘UC-157’ (Krarup and Henzi, 1993; Krarup, 1996; González and del Pozo, 1999; 2002).The UC-157 variety is one of the most widely cultivated as green asparagus in warm to temperate climate zones. Assays have been carried out in several localities, searching for new variety alternatives, using ‘UC-157’ as control (Carballo et al., 1992; McCormick and Thomsen, 1995; Mullen et al., 1996; Cueto and Lesnick, 1999; Garrison et al., 1999; Mullen et al., 1999; Stone and Roose, 1999; Drost, 2002; Mullen et al., 2002). Besides the International Assays of Asparagus Varieties organized by the International Horticultural Society Workgroup (Knaflewski, 1996; Paschold et al., 1996; Van Oordt et al., 1999; Benson, 2002; Jinsong, 2002). In general, the ‘UC-157’ yield is very low in cold climate localities of Europe, where German and Dutch varieties predominate (Knaflewski, 1996b; Paschold et al., 1996). Since the beginning of the ’90 decade, varietals assessment has been carried out in different zones of Chile, with the purpose of finding new asparagus cultivars that could replace or complement ‘UC-157’ (Krarup and Henzi, 1993; Krarup, 1996; González and del Pozo, 1999; 2002). The Second IACT was established in 1994 in the Central Zone (Metropolitan Region, 33°40’ lat. South) and South Zone (Xth Region, 39°48’ lat. South) of Chile. Among 14 asparagus cultivars assessed in the central zone, ‘UC-157’ reached first place in commercial yield. Among 27 cultivars assessed in the South, ‘UC-157’ occupied the fifteenth place, after eight harvest seasons in both assays (Benson, 2002). The first place in the southern zone was reached by ‘Jersey Giant’.
In the VIIIth Region (36°29’ lat. South) preliminary results indicated that the commercial yield of ‘UC-157 F2’ was similar to that of ‘Jersey Giant’ and ‘Jersey Knight’, but higher than ‘Apollo’ (González and del Pozo, 1999). In another trial, where some German varieties were compared to the Californian varieties ‘Atlas’, ‘Apollo’, and ‘Grande’, the ‘UC-157 F2’ control was exceeded by the latter, both in total as well as commercial and export yields, but not by the German varieties (González and del Pozo, 2002).
The purpose of this trial was to compare the behavior in yield and quality of some promising asparagus cultivars of the Jersey and other types from California, to UC-157 F1’ and ‘UC-157 F2’.
MATERIALS AND METHODS
The trial was established on December 21 1999, using 14 week old plantlets obtained in the greenhouse in the Quilamapu Regional Research Center of the National Institute of Agricultural Research, Chillán (36°32’ lat. South; 71°55’ long. West), in a soil of volcanic origin classified as Dystrandepts. The climate is a typical Mediterranean one, mean yearly precipitation 1,200 mm and average yearly temperature 13.1°C, minimum 3.0°C in July and maximum 28.6°C in January (del Pozo and del Canto, 1999).
The experimental design was of completely randomized blocks, four repetitions, and plots constituted by four 6 m long rows. The planting distance was 1.5 m between rows and 0.2 m between plants in the row, and a planting depth of 20 cm. Cultivars evaluated were: ‘Atlas’, ‘Grande’ and ‘Apollo’ of Asparagus Seeds and Transplants (California) (Benson et al., 1996), ‘Jersey Giant’ (Ellison and Kinelski, 1985), ‘Jersey Gem’, ‘Jersey General’, ‘Jersey King’, ‘Jersey Knight’, and ‘Jersey Supreme’ of Jersey Asparagus Farms (New Jersey) (Ellison et al., 1990), and the controls ‘UC-157’ F1 and F2.
The soil was fertilized before planting, with 138 kg ha-1 P2O5, 50 kg ha-1 K2O and 48 kg ha-1 N, applied as triple superphosphate, muriate of potash, and sodium nitrate respectively. One month after planting, an application of 48 kg ha-1 N took place. During the second year (2001) 135 kg N ha–1 were applied as sodium nitrate; on the third year (2002) 180 kg N ha–1 as potassium nitrate; the fourth year (2003) 135 kg N ha–1 as sodium nitrate; the fifth year (2004) 135 kg N ha–1 as urea and in the sixth year (2005) 80 kg N ha–1 as potassium nitrate were applied, divided in three equal portions during the summer (aerial growth period). During the first year, weeds were controlled manually, and from the second year on, metribuzine (1 L i.a. ha-1) was applied during winter, before harvest, continuing with hand weeding during and after harvest, complemented by rotary tiller passes between the rows. Plants received furrow irrigation after harvest, until March of the next year, on an average of seven irrigations per season.
The plots were harvested from Mondays to Saturdays from the first appearance of spears, until October 12 on 2001; December 2 on 2002; November 29 on 2003; December 3 on 2004, and December 2 on 2005. Spears were weighed immediately after harvest, before cutting and selection, this was the field yield. Later on, the spears were cut to 18 cm long and were weighed to determine the total yield. Total yield was composed of the commercial yield and rejects; the commercial yield was divided into exportable yield and “País” or domestic market portion. The reject was formed by spear having a diameter below 7 mm, open tips, twisted (angle > 90º), severely damaged by insects, diseases or frost. The “País” category was composed of spears less twisted than the hulls (between 45 and 90°), flat, with slight damage from larvae and slugs, stained by Stemphylium vesicarium and/or those where bud scales had started to open (swollen tip). The remainder of the commercial quality was made up by exportable calibers (diameter > 7 mm), tight heads and no damages. The export market spears were divided into two categories: those with a diameter (measured 2 cm away from the cut) between 7 and 17 mm (Small, Standard and Large) and the ones thicker than 17 mm (Extra Large and Jumbo).
The results obtained were subjected to variance analysis, comparing means through a least significant difference (LSD) test with the statistics program IRRISTRAT (IRRI, 2003). ]]>
RESULTS AND DISCUSSIONJ. Supreme cultivar showed the uppermost accumulated yield of five seasons in all categories (field, total, commercial and export markets). The variety showing the lowest yield was Apollo, which did not differ statistically from some Jersey type cultivars, but was below the controls ‘UC-157’ F1 and F2 (Table 1). During trials carried out in Michigan and harvested through seven seasons, “J. Supreme” was the variety with the highest yield among 36 cultivars evaluated (Garrison et al., 1999). It has also been pointed out as one of the most promising varieties for the Connecticut area of the United States (Elmer et al., 1999). The main disadvantage of ‘J. Supreme’ as well as that other varieties of the Jersey type, is the intense antocianin coloration of its bud scales - this would limit its export as fresh produce but not when frozen - as this includes a blanching process which eliminates this color and turns it to green.
The lack of differences between the yield of the control ‘UC-157 F1’ and ‘J. Giant’ (Table 1), which is catalogued as a variety with intermediate yield as compared to ‘UC-157 F1’, considered of low yield, on the basis of the photosynthetic efficiency of its foliage (Faville et al., 1999) is noteworthy. However, in the Second International Asparagus Cultivar Trial, where both varieties were used as controls ‘UC-157 F1’ was superior in commercial yield to ‘J. Giant’ in five of the six temperate climate localities used as trial sites, and in two of them it occupied the first place (Benson, 2002). ‘UC-157’ may possibly have a better adaptation capacity to different environments. In this regard, Contreras and Krarup (2000) determined that ‘UC-157’ F1 and F2 were the cultivars with better capacity of response to environmental improvements, as compared to ‘Atlas’, ‘J. Giant’ and ‘Mary Washington’.
Table 1. Cumulative yield of different asparagus cultivars over five harvest seasons (2001-2005).
Cuadro 1. Rendimiento acumulado de diferentes cultivares de espárrago en cinco temporadas de cosecha (2001-2005).
In former trials (González and del Pozo, 1999; 2002) ‘UC-157 F2’ always showed a lower yield than ‘UC-157 F1’, but this condition was not observed in this case (Table 1). ‘UC-157 F1’ is a clonal hybrid, product of the crossing of two varieties that are not homozygous, and both descending from the older north-American cultivar Mary Washington (Knaflewski, 1996a), so some seeds coming from a plantation of this hybrid could eventually give similar yield results. In this case, the ‘UC-157 F2’ seeds were collected from vigorous ‘UC-157 F1’ plants, and this could explain the good results. During a study carried out in Chillán, the aerial and subterranean growth of both cultivars was assessed during the first year and no differences were observed between ‘UC-157 F1’ and ‘UC-157 F2’ in any of the parameters evaluated (Pertierra et al., 2006). On the other hand, it is well known that it is very difficult to distinguish between a F1 and a F2 of a clonal hybrid. This fact has led the search for molecular markers of different alleles for which the parents of that hybrid cultivar would be homozygous (Roose and Stone, 1996).
The J. Supreme cultivar had the highest yield from the first harvest season, and showed a marked difference from the rest of the varieties only from the second year (Table 2). The behavior of asparagus in the first harvest year may not be a good indicator of what could happen later on. This is clearly seen in the commercial yield of ‘Apollo’; it was the lowest of all, starting from the second year, although it was among the highest during the first year. The correlation coefficient between the yield in the first year (2001) and in the last year (2005) was 0.55, and a linear regression gave a R2 equal to 0.3. The correlation coefficients between the first year and the intermediate years (2002 to 2004) were smaller, varying from 0.24 to 0.27. This shows the lack of relationship between the yield obtained during the first year and the following years. In a previous trial where ‘J. Supreme’ was included but which was assessed during two seasons only due to an intense Fusarium attack, showed a commercial yield slightly superior to controls ‘UC-157’, but the export yield was lower than the controls (González and del Pozo, 2002). In almost all varieties, a decrease in commercial yield was observed during the last season, except for ‘J. Giant’ which maintained its yield of the previous year (Table 2).
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When analyzing production over time during the last harvest season (Figure 1) it can be seen that the controls ‘UC-157’ started harvest during the last week of August, and were met by J. Supreme’ as to volume produced towards the end of September; the latter becoming quickly differentiated from the rest of the varieties. Production of all varieties fell down during October, due to the drop of mean temperatures below 10ºC (Keulder and Riedel, 1996). ‘J. Supreme’ and ‘Apollo’ can be differentiated easily from the rest of the varieties in Figure 1, as they show extreme yields, but ‘UC-157 F1’ can also be distinguished in the upper section of the group.
Figure 1. Cumulative total yield of asparagus cultivars during 2005 harvest season, and mean temperature during the harvest period.
Figura 1. Rendimiento total acumulado de las variedades de espárrago en la temporada de cosecha 2005 y temperatura media del período de cosecha.
The number of spears harvested per surface unit, which is the main yield component in asparagus, was much higher in J. Supreme variety from the second year on (Table 3), and coincides with what is determined in commercial yield (Table 2). The ‘UC-157’ controls followed ‘J. Supreme’ as to the total of spears harvested during the five seasons, but did not differ from ‘J. Giant’ (Table 3). ]]>
Table 3. Number of harvested spears of different asparagus cultivars per unit area, over five harvest seasons (2001-2005).
It is important to evaluate the proportion of thin spears (diameter 7-17 mm) in the production, as foreign markets now prefer this type of caliber rather than thick spears. ‘J. Supreme’ and the ‘UC-157’ control varieties were uppermost in this respect, as they produced a larger percentage of thin spears and an export production superior to the average of all cultivars. J. Giant, J. King, and Apollo cultivars also had a high proportion of thin spears, but their export yield was low (Figure 2).
Figure 2. Relationship between cumulative exportable yield in five seasons (2001-2005) and percentage of exportable spears with 7-17 mm diameter (average of five seasons, 2001-2005). Perpendicular lines in each axis correspond to the average of all cultivars. LSD (P ≤ 0.05) of exportable yield is 3.84, and of the percentage of 7-17 mm spears is 6.56. LSD: Least significant difference.
Figura 2. Relación entre el rendimiento exportable acumulado de cinco temporadas (2001-2005) y el porcentaje de turiones exportables de 7-17 mm de diámetro (promedio de cinco temporadas, 2001-2005). Las líneas perpendiculares en cada eje corresponden al promedio de todos los cultivares. DMS (P ≤ 0,05) de rendimiento exportable es 3,84 y del porcentaje de turiones de 7-17 mm es 6,56. DMS: diferencia mínima significativa.
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The proportion of the total production destined to the domestic market (País) and the discards varied in every season, depending on environmental conditions. Table 4 shows the five seasons average percentage of “País” production and its causes; it can be appreciated that this production fluctuated by about 40%, the Californian varieties showing the lowest percentages. The main causes of the production destined to the domestic market were open and twisted spears. In this respect the ‘UC-157’ controls were singled out by a lesser proportion of open spears. Male asparagus plants tend to branch out at a lower height than female plants (Roose and Stone, 1999); this would explain the greater proportion of open spears in the Jersey-type varieties, which have only male plants, as compared to ‘UC-157’, which has male and female plants in similar proportions. Another difference between male and female plants is that the former produce 80% more spears than the second, because the weight of the root system, the carbohydrate content and the number of buds on the rhizome of male plants are much higher than those of female plants (Sinton and Wilson, 1999). This aspect would favor the varieties having male plants only, as is the case of ‘J. Supreme’.
Table 4. Criteria for the selection of spears for the domestic market (País) and their percentages as to the total yield, in different asparagus cultivars. Average of five harvest seasons (2001-2005).
Cuadro 4. Causas de selección de los turiones para el mercado interno (País) y sus porcentajes en el rendimiento total, en diferentes cultivares de espárrago. Promedio de cinco temporadas de cosecha (2001-2005).
The third cause determining the “País” production was the purple spot (Stemphylium vesicarium), whose intensity of attack varied during the different harvest seasons (Table 5), depending on spring environmental conditions, and favored by high relative humidity. The larger effect of this disease upon yield took place during 2004, when all varieties suffered an attack of over 20% with the exception of ‘J. Gem’, during all seasons this was the one that suffered the less, with the smaller percentage of stained spears at the end of the five seasons (Table 4). The year 2001 is at the other extreme, the disease did not show up and therefore does not appear in Table 5. No resistance to S. vesicarium has been detected in the improved varieties and significant differences in the susceptibility to this disease have been identified, the French varieties being much more susceptible than the North-American ones (Broadhurst, 1996). Generally speaking, the damage is greater when the attack takes place in summer, affecting the foliage; this can cause a loss of up to 20% of the yield in J. Giant and J. Knight varieties if it is not controlled with fungicides (Meyer et al., 2000). Summer attacks are quite unusual in Chillán; this is generally a dry season in this zone.
Table 5. Total production of spears damaged by purple spot in different asparagus cultivars during five harvest seasons (%)1. ]]>
Cuadro 5. Producción total de turiones dañados por mancha púrpura en diferentes variedades de espárrago durante cinco temporadas de cosecha (%)1.
The average levels of rejects for the five seasons fluctuated between 7.8 and 14.3% of the harvested total, although it rose over 20% in some years (data not shown). The main causes of reject were malformed and damaged spears, also those affected by frost, especially in some seasons. The varieties that showed a lesser proportion of spears affected by frost started harvest a little later than those which were more strongly affected, as was the case of the controls ‘UC-157’ and ‘Atlas’, which are early (Figure 1). The reject caused by open spears was not important, and did not exceed 1.8% of the total production. As was the case with the País category, the ‘UC-157’ controls showed a lesser proportion of open spears, but did not differ from Californian variety ‘Grande’.
CONCLUSIONS
The Jersey Supreme hybrid appears to be a good alternative, due to its high commercial yield, very superior to that of all varieties assessed. However, its quality is inferior to that of ‘UC-157’, due to both the antocianin coloration of the bud scales and the propensity of the spear to open at a low height; these aspects would make it suitable for frozen produce market only.
The UC-157 variety at present in use in Chile is still the best alternative for the fresh market; its yield is similar to that of other varieties although lower than that of ‘Jersey Supreme’.
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