Pithy pear fruit are not distinguished externally from sound fruit and thus often cause unexpected economic losses. To find out the cause of pithiness, the pithiness incidence and characteristics of Japanese pear (Pyrus pyrifolia cv. Niitaka) fruit picked from a spot frequently produced pithy fruit in an orchard were compared with those of fruit picked from another spot produced sound fruit every year. And the soil chemical properties of the two spots and mineral contents in fruit, shoots, and leaves of Japanese pear trees cultivated in the two spots were also examined.
The pithiness incidence was 0, 8.8, and 11.3% at 7 days before and 0 and 7 days after optimal harvest date, respectively, in the spot frequently produced pithy fruit. Flesh firmness was significantly lower in pithy fruit than in sound fruit, while soluble solids content was slightly higher in pithy fruit than in sound fruit. Unlike other mineral contents, Ca content was significantly lower in pithy fruit than in sound fruit. These results indicate that Ca deficiency in fruit is closely associated with decrease in flesh firmness and thus pithiness development. Ca content in soil of the spot frequently produced pithy fruit was also significantly lower than that in soil of the spot produced sound fruit. However, shoots or leaves did not exhibit significant difference in Ca and/or other mineral contents between the two spots, indicating that Ca deficiency in fruit is dependent on the translocation of Ca within a plant rather than soil Ca status. Although total-N, available P2O5, K, and Ca contents were significantly lower in soil of the spot frequently produced pithy fruit than in soil of the spot produced sound fruit, Mg and Na contents and pH were not different between the soil conditions.
Fruit maturity and Ca level in fruit are closely related to the incidence of pithiness in ‘Niitaka’ Japanese pear.
Pithiness in Japanese pear fruit is a serious physiological disorder that deteriorates flesh texture (Chijiwa
Since the cell membrane permeability of the pithy fruit flesh is higher than that of healthy flesh, pithiness may be associated with an aging process. As pithiness intensifies, affected flesh tissues form cavities, decreasing the specific gravity and the flesh firmness of fruit during their ripening (Chijiwa
The pithiness symptom in Japanese pear occasionally arises in the later-picked fruit (Kajiura
Pithiness as in the case of other physiological disorders in fruit (Bangerth, 1979; Ferguson
In the present study, the soil chemical properties of one spot frequently produced pithy fruit in a Japanese pear (
Two spots of an orchard in Ichon, Korea were selected to investigate pithiness incidence and characteristics in fruit of 12-year-old Japanese pear (
Chemical properties of soil sampled from the two spots in late July were analyzed with respect to pH, organic matter, and mineral contents including total-N, available P2O5, K, Ca, Mg, and Na. The analysis was replicated three times for each spot. Each soil sample was collected from 20 to 30 cm below the soil surfaces of three points at a distance of 1.5 m from a tree. Soil pH of a mixture of soil and water (1:5, w/v) was determined using a pH meter (D-24, Horiba, Kyoto, Japan). Organic matter, total-N, and available P2O5 in soil were analyzed according to the methods of Tyurin, micro-Kjeldahl, and Lancaster, respectively (RDA, 1988). The contents of exchangeable cations including K, Ca, Mg, and Na were determined by analyzing eluted solution from soil using an inductively coupled plasma emission spectrometer (ICPS-1000IV, Shimadzu Corp., Kyoto, Japan). Four shoots, 50 leaves, and 5 fruit per tree were also randomly collected from the two spots to examine their mineral contents including total-N, P, K, Ca, and Mg. The analysis of mineral contents in shoots, leaves, and fruit were replicated three times. The shoots and leaves were sampled in late July and the fruit in mid-October. Total-N was analyzed using a Kjeltec auto 1035 analyzer system (Foss Tecator AB, Hoganas, Sweden). The vanadate method was used for P analysis (RDA, 1988). K, Ca, and Mg contents were determined using an atomic absorption spectrophotometer (AA680, Shimadzu, Kyoto, Japan).
At optimal harvest date, October 15, 2006, and 7 days before and after the optimal harvest date, pithiness incidence in fruit picked from the spot frequently produced pithy fruit was examined to find out the correlation with fruit maturity. The optimal harvest date in Ichon, Korea was determined based on the days after full bloom and flesh firmness (Childers
Pithy fruit were not found in the spot produced sound fruit every year. In the spot frequently produced pithy fruit, however, pithiness occurred as much as 0, 8.8, and 11.3% at 7 days before and 0 and 7 days after optimal harvest date, respectively (Table 1). These results indicate that targeting the harvest date is very important in ‘Niitaka’ Japanese pear, because pithiness is known to develop on the tree as well as during storage (Kajiura
Incidence of pithiness according to harvest date in spot frequently produced pithy fruit of Japanese pear (P. pyrifolia cv. Niitaka)
Fruit weight and Hunter values of pithy fruit were not significantly different from those of sound fruit (Table 2), demonstrating that pithy fruit was not distinguished externally from sound fruit. Flesh firmness, however, was obviously lower in pithy fruit than that in sound fruit, while soluble solids content was slightly higher in pithy fruit than in sound fruit (Table 2). In pears, a decrease in flesh firmness is usually correlated with cell wall degradation during ripening (Hiwasa
Characteristics of pithy and sound fruit of Japanese pear (P. pyrifolia cv. Niitaka) harvested at optimal date (October 15)
The incidence of pithiness on the tree as well as during storage could be modified by preharvest environmental conditions and cultural practices during growing season. The preharvest factors include seasonal characteristics such as temperature during growth and rainfall, orchard characteristics including tree and soil conditions, application of agro-chemicals, irrigation, and geographical position, and the position of the fruit in the tree (Ferguson
Several physiological disorders in fruit have been associated with low Ca and/or with excess of N (Ferguson
Mineral contents in the peel and the flesh of pithy and sound fruit of Japanese pear (P. pyrifolia cv. Niitaka) harvested at optimal date (October 15)
High N level in fruit, also influencing structural integrity of fruit tissues, could deteriorate fruit qualities in association with pithiness development. In the present study, sound fruit tended to have higher total-N than pithy fruit, although significant difference was not observed in pithy and sound fruit in total-N contents (Table 3). Sound fruit, however, showed lower N/Ca ratio than pithy fruit, suggesting that N/Ca ratio as well as N level are important in pithiness development of ‘Niitaka’ Japanese pear.
Mineral level in a plant can be affected by mineral level in soil. The contents of total-N, available P2O5, K, and Ca were significantly lower in soil of the spot frequently produced pithy fruit than in soil of the spot produced sound fruit (Table 4). Mg and Na contents and pH in the two soil conditions were not different (Table 4). Furthermore, the mineral contents including Ca in shoots and leaves were not significantly different between the two spots, having little or no relation to soil mineral status (Table 5). These results suggest that Ca-related physiological disorders in fruit might be due to an inefficient translocation of Ca rather than poor Ca uptake (Bangerth, 1979). This problem is illustrated by the observation that leaves or shoots contain considerably higher Ca than storage organs irrespective of orchard position (Tables 3, 5). Ca differs from other minerals by being imported into fruit only in small amounts, much less than into leaves. However, the translocation of Ca within the tree and the cause of Ca deficiency in fruit are still a matter of conjecture (Scaife and Clarkson, 1978; Ferguson
Chemical properties of soil from spot produced pithy or sound fruits of Japanese pear (P. pyrifolia cv. Niitaka)
Mineral contents per dry weight in shoots and leaves of Japanese pear (P. pyrifolia cv. Niitaka) produced pithy and sound fruit