Letícia AF: New self-compatible plum cultivar resulting of a mutation of LaetitiaAbstract:
Letícia AF is a mutation of the plum cultivar Laetitia that confers self-compatibility. This work compared the Letícia AF mutant cultivar with the standard Laetitia regarding fruit set, self-compatibility, yield, and fruit quality traits during four growing seasons. The study was carried out in two plum orchards with the cultivar Letícia AF (orchard 1) and Laetitia plus pollinizers trees (orchard 2) and in an experimental unit with Letícia AF and Laetitia planted side by side. A self-compatibility test was performed on covered branches to prevent pollinating insects from reaching the flowers. Fruit set occurs in covered branches of Letícia AF, whereas it was rare in Laetitia. In commercial orchards, Leticia AF plums yield was higher than that of Laetitia over the years. The results suggest that the oscillation in productivity across the years, mainly due to unfavorable conditions for insect pollination, may be lower in the plum Leticia AF orchard. On the other hand, the requirement for fruit thinning may be greater in Leticia AF. No significant differences were found between the mutant and the standard cultivar regarding fruit quality at harvest and after 30 days of cold storage, indicating the mutation did not alter the fruit characteristics.
Index terms
Prunus salicina; self-compatibility; fruit set; pollination
Resumo:
Letícia AF é resultante de uma mutação do cultivar de ameixeira Laetitia (Letícia, no Brasil) que confere a característica de autocompatibilidade. Neste estudo, comparamos o cultivar mutante Letícia AF com o original, com relação a pegamento de frutos, características vegetativas, produtividade e qualidade de fruto, durante quatro safras. O estudo foi conduzido em dois pomares comerciais com os cultivares Letícia AF (pomar 1) e Laetitia, com plantas polinizadoras (pomar 2), e uma unidade experimental com plantas de Letícia AF e Laetitia lado a lado. Um teste de autocompatibilidade foi realizado com ramos cobertos para impedir o acesso de insetos polinizadores. Houve pegamento de frutos em ramos cobertos de Letícia AF, ao passo que, em Laetitia, isso é raro. A produtividade foi maior em Letícia AF do que em Laetitia, ao longo dos anos. Os resultados sugerem que a oscilação na produtividade, ao longo dos anos, principalmente devido a condições desfavoráveis para a polinização, seja menor em Letícia AF. Por outro lado, a mutação para autocompatibilidade induziu alto índice de pegamento de frutos e, consequentemente, maior demanda por raleio. Não foram encontradas diferenças significativas entre o cultivarmutante e o original,em termos de qualidade de frutos, tanto na colheita como após 30 dias deconservação a frio, indicando que as características de fruto não foram alteradas pelamutação.
Termos para indexação
Prunus salicina; autocompatibilidade; pegamento de frutos; polinização
Introduction
The plum cultivars Laetitia and Fortune, account for most of the plum production in southern Brazil. Laetitia originated in South Africa by the Fruit and Fruit Technology Research Institute and was officially released in 1984 as Laetitia (FFTRI, 1984). In Brazil, it became known by the Portuguese name of Letícia. It was introduced at the Epagri - Videira Experiment Station in 1985, and its diffusion began in the early 1990s. Growers widely accepted it for combining high fruit quality and relatively high resistance to leaf scald, caused by the bacterium Xylella fastidiosa (DUCROQUET et al., 1994). The emergence of this cultivar made it possible the plum production to rise again in Brazil in the 1990s, after a long period of decline since the introduction of leaf scald in the 1960s.
Nowadays, it is Brazil’s primary late-ripening plum cultivar, with the harvest in mid to late January.
Laetitia is considered a self-incompatible (i.e., self-unfruitful) cultivar (FFTRI, 1984, DUCROQUET et al., 1994), and its cultivation is only possible with the presence of pollinizer cultivars, which occupy between 10 and 20% of the orchard area. The occurrence of periods with unfavorable conditions for the action of pollinating insects in the flowering period has been the most common cause of low yield in commercial Laetitia orchards in Brazil. The risk of losses is aggravated by the application of products to break dormancy, which tends to concentrate the flowering period.
Another factor that affects pollination is the occurrence of high temperatures during flowering. Dry and warm weather, with temperatures above 30°C, are more common during the “La niña” phenomenon and result in low fruit setting, even if pollinating insects can work normally. Because of its late flowering, Laetitia is more subject to periods of high temperature during the flowering period.
In this work, we present a self-compatible mutation of the plum cultivar Laetitia that does not require cross-pollination. This new cultivar is registered as Letícia AF and has been available for planting since 2022.
Material and Methods
A self-compatible mutation of Laetitia was found on the property of the fruit grower Hermes Coser, in the municipality of Videira, SC, who observed that the material was more productive even in the absence of other cultivars nearby. Two orchards of Laetitia and Leticia AF (the mutant) on peach seedlings rootstock established in Videira, Santa Catarina State, southern Brazil, were used in the study. Plants were at 2×5 m spacing and trained to a “V” system. Orchard practices (mineral fertilization, insect and disease control, pruning, and growth regulator for dormancy release) were standard for Southern Brazil plum production (DALBÓ, 2021). Orchard 1 (Leticia AF) of approximately 1 ha was established at Hermes Coser property with Leticia AF (mutant) without pollinizer trees.
Orchard 2 (Laetitia) of approximately 1 ha, established at Divo Galli grower property with Laetitia (standard cultivar), approximately 500 m far from orchard 1, was used for comparisons. In orchard 2, the cultivar ‘SA86-13’ was planted as pollinizer within each row of Laetitia trees; one pollinizer tree for each group of nine Laetitia trees.
These orchards 1 and 2 were planted in 2016 and 2015, respectively. Additionally, five trees of each Laetitia and Leticia AF cultivar, planted side by side in 2020 at EPAGRI – Videira Experiment station (orchard plot 3), were used for this study. The fruits from orchards 1 and 2 were harvested following commercial practice at the commercial maturity stage, and the fruit mass of the entire area was quantified annually and expressed by metric ton per hectare. Additionally, the annual plum yield from other commercial orchards in the Videira region was estimated based on IBGE database.
The fertilization capacity of the flowers without cross-pollination was evaluated by bagging branches with transparent fabric (“Voil”) to prevent pollinating insects from reaching the flowers. During the flowering period of the years 2019 and 2020, four branches containing 80 to 120 floral buds not yet opened were bagged, both in the orchard of Leticia AF (orchard 1) and in plants of Laetitia, at Videira Experiment Station. After the natural fall of the petals, the covered bags were opened, and the fruit were counted when they reached the size of one centimeter.
In 2021, 100 fruits from the Letícia AF orchard (orchard 1) and from Laetitia plants from the neighboring orchard (orchard 2) were collected to compare the fruit characteristics at harvest and after storage. This evaluation was repeated in the following harvest (2021), collecting the same number of fruits from both cultivars. The fruits were evaluated at harvest and after 30 days of storage at 1°C, followed by a three-day shelf life at 22oC. Fruit samples for air storage were placed in opened plastic boxes lined with perforated low-density polyethylene bags (20 μm = 10 μm per wall). Flesh firmness, soluble solids content, titratable acidity, skin color, and disorders incidence were assessed as previously described (ARGENTA et al., 2003). Reading of fruit surface color was taken between exposed and shaded fruit sides on the equator using a 1 to 10 scale color chart (1 = green, 10 = purple) (ARGENTA et al., 2023).
Data were subjected to analysis of variance (ANOVA), and the means were compared by Tukey’s HSD test (P < 0.05) using the Statistical Analysis System (SAS software Version 9; SAS Institute, Cary, USA). A non-parametric Kruskal-Wallis test was performed for productivity data specifically, using each year’s data as replicates, considering that this variable’s assumptions of normality and homogeneity of variances were not satisfied.
Results and Discussion
The branches covered in the flowering period of standard Laetitia did not produce fruits in their great majority (Table 1). The exception was a single fruit on one of the branches in 2020. This result shows that Laetitia is not totally self-incompatible, but the degree of self-fertilization is very low, as already indicated by some reports from producers and the literature (FFTRI, 1984). In Letícia AF, the average number of fruits formed per covered branch was 4.0 in 2019 and 6.5 in 2020, being significantly higher (p<0.001) than standard Laetitia and indicating that there is fruit formation without the participation of insect pollinators. The environmental conditions in covered branches are different and probably less favorable for pollination and fruit formation than in open branches.
The validation of this behavior could be verified in the commercial orchard established in an area of about 1.0 ha in the absence of pollinating cultivars (orchard 1) (Table 2). In 2020, productivity was around 10 t.ha-1, but the plants were still young (first crop). In the 2020/21 harvest, there was a need for thinning, and productivity reached 35 t.ha- 1, even with losses due to excessive rainfall during the harvest period and without the plants having reached their full production potential. In the 2021/22 harvest, productivity was around 60 t.ha-1, due to a very high effective fruit set and the grower’s difficulty in thinning it properly. As a result of the high productivity and a moderate water deficit close to maturation, the average fruit size was below the desirable level, with only 40% of the fruits classified as large, with a higher market value. In the following harvest (2022/23), weather conditions were very unfavorable due to temperature fluctuations in the winter period and occurrences of two late frosts. There were some losses in the Letícia AF orchard due to late frost in the lower part of the orchard, which occupies about 25% of the area. Even so, productivity was normal in the rest of the area, estimated at around 35 t.ha-1.
The productivity of the Letícia AF (orchard 1) commercial orchard can be considered high in all evaluated seasons (Table 2). The same did not occur in the comparison orchard (orchard 2) and in most plum orchards in the Midwest region of Santa Catarina State. The flowering period in 2019 and 2020 coincided with periods of dry heat. with temperatures reaching maximums of 37°C at the Videira Experimental Station. which is located close to and with similar conditions to the evaluated orchard (Figure 1). In these two harvests. there were reports of low productivity in most of the Laetitia orchards in the region. which can be attributed to this factor since there were no limitations to the action of pollinating insects. This can also be observed in the orchard closest to the standard Laetitia (orchard 2). where productivity in these two years was lower than Letícia AF orchard (Table 1).
Maximum daily temperatures in the spring of 2019, 2020, and 2021, Videira, SC. The blue bar indicates the entire bloom period in this study's Letícia AF and Laetitia orchards. Days with maximum temperature higher than 30ºC are highlighted in yellow.
In the 2021/22 harvest,productivity was considered normal; however, in the following harvest (2022/23), productivity in general was low, both in the orchard used for comparison (orchard 2) and in most orchards in the region, due to high temperatures in the winter period and occurrences of late frosts. The same effect was observed for plum productivity in the whole municipality of Videira and is documented in the archives of the local office of IBGE. This statistical office collects data on economic activities (Table 2). The IBGE data includes all plum cultivars. most of them self-incompatible.
It reports the same reduction in productivity observed in Orchard 2 (Laetitia) in the first two years, which can be attributed to dry heat stress conditions during the flowering period (Figure 1). In 2021, during most of the days at bloom time. the maximum temperatures were below 30°C (Figure 1), in a range less suitable for heat stress in stone fruits (CARPENEDO, 2017). The harmful effect of heat stress periods on the reproductive structures of peaches has been reported in Brazil (NAVA et al., 2011; CARPENEDO et al., 2020) and probably the same is happening in plums. The low productivity in the Laetitia orchard. likely due to adverse weather conditions in 3 out of 4 years. highlights the difficulty of establishing profitable commercial plum production in this subtropical region. Nevertheless. the higher yield and stability of production over the years in the Leticia AF orchard are clear advantages of this new cultivar compared to the Laetitia cultivar.
The comparison between Letícia AF and Laetitia was also made with plants of the same age and located side by side at the Videira Experimental Station. It was observed that the plants of the two cultivars had good vegetative development and produced flowers in the second year. However, only Letícia AF had fruit set, requiring intense thinning. In the case of Laetitia, all the flowers aborted. In the third production season (2022-23). losses due to late frosts were very severe for both cultivars and data was impossible to collect. However, observations from the second year of these plants and the high productivity of the commercial orchard indicate that the mutation for self-compatibility also induces a greater fruit set and a greater need for thinning.
Thus,the chemical thinning becomes very important for Letícia AF. and studies in this direction are needed to facilitate commercial cultivation.
The fruits of Letícia AF and standard Laetitia did not show obvious differences in appearance and quality. The average fruit size of Letícia AF was similar to that of Laetitia despite the greater fruit load in Letícia AF trees (Table 3). At harvest (day 0), the fruits of both cultivars did not differ in terms of flesh firmness in 2021 and soluble solids content (SS) and acidity in 2022 (Table 3). Leticia AF fruit had slightly lower SS contents than Laetitia in 2021. In 2022, Leticia AF and Laetitia fruits differed in firmness at harvest but not after storage. There was no flesh browning in the fruit of both cultivars after storage. The result shows no consistent difference in fruit maturity and quality between Leticia AF and Laetitia at harvest and after storage.
Conclusion
Letícia AF is a self-compatible (self-fruitful) mutation of the plum cultivar Laetitia. The higher fruit yield by Letícia AF compared to standard Laetitia was associated with a greater fruit setting. The result suggests that the fruit setting in Letícia AF may be less affected by adverse weather conditions for pollination.
No significant and consistent differences were found between Leticia AF and Laetitia regarding fruit quality at harvest and after storage.
References
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» https://doi.org/10.1590/S0100-29452011005000065
Edited by
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Willian Krause
