*3.1. Rootstock Effect*

Fruit growers use different rootstocks to match the tree vigour to the climatic, soil and agricultural conditions [37]. In apples, the rootstock also influences the speed of fruit ripening and thus the date of harvest [38]. However, in this study, the ripening speed and the harvest date were hardly affected by the rootstock type (Table 1). The Streif index, which is considered a good indicator of harvest maturity [39,40], varied little in the discussed experiment. There were no index differences in 2013, and very small differences in the other two years. The starch index, which affects the Streif index most strongly, also showed only slight, although significant, differences. Differences in firmness between the fruit coming from trees grown on different rootstocks were very small as well. No firmness differences were found in two years (2011 and 2012), and a significant difference, although of only 2 N, was identified in 2013.

**Table 1.** The influence of rootstock on the quality parameters of pears at harvest in 2011–2013.


<sup>1</sup> One-way analyses of variance; data in the same column marked with the same letter, separately for each year of experiment, are not significantly different at α = 0.05 (Duncan's test). Q S1—Quince S1 rootstock; PC—Pyrus caucasica Federov rootstock; PD—Pyrodwarf rootstock.

> A study assessing the influence of six rootstocks on the TSS of 'Forelle' pears found that the differences in TSS at harvest were very small and did not exceed 0.5◦ Brix within two years [10]. TSS differences were also small in our study. No differences were detected in the first year of the experiment, and even though they occurred in the two subsequent years, they were rather incidental and random. Total acidity followed a clearer pattern and was the lowest in fruit from trees growing on *Pyrus caucasica*. However, the TSS/TA ratio, which is crucial for the subjective perception of fruit taste [41], did not vary considerably between fruit from trees grown on different rootstocks.

> As the present study did not show any significant and long-term influence of the rootstock on the basic quality features of pears, this factor was omitted in our further analyses regarding storage and storability, except for mass loss (Tables S1–S12).

#### *3.2. Mass Loss*

Fruit mass loss during storage depends on a number of factors occurring both before and after harvest, such as the content of minerals (especially calcium) in fruit, fruit maturity at harvest, incidence of diseases and disorders, and storage conditions [11]. As all fruit analysed in the present study grew under the same conditions and was treated in the

same way at the time of harvest, and its selection was entirely random, in line with the experimental design, it can be assumed that the loss of fruit mass was influenced only by the experimental factors. All factors applied in this study affected the loss of fruit mass during storage (Tables 2–4). The rootstock may affect the quality parameters of fruit [42], as well as the speed and time of ripening [43]. In 2011, the effect of the rootstock type on the mass loss of stored fruit was significant from the first measurement until the 120th day of storage, but this factor became less and less significant with time. In the following year, no such effect was found, but it was observed that the interaction between rootstock and 1-MCP application had a very strong influence on transpiration. This interaction did not decrease with time, which means that 1-MCP application was the predominant factor. In 2013, the rootstock clearly affected the loss of fruit mass during the storage period, except the first month after 1-MCP treatment. The interaction between rootstock and 1-MCP application was weaker, such as in the first year, and was significant only in the middle of the storage period.

**Table 2.** Mass loss (%) of non-1-MCP-treated (control) and of 1-MCP-treated 'Conference' pears after storage in normal (NA) and controlled (CA) atmosphere in 2011.


<sup>1</sup> Numbers in parentheses are the standard deviation of the mean (n = 10). <sup>2</sup> *p*-value of F ratio: ns—not significantly different; \* *p* < 0.05; \**\* p* < 0.01; \*\**\* p* < 0.001. Q S1—Quince S1 rootstock; PC– Pyrus caucasica Federov rootstock; PD—Pyrodwarf rootstock. NA—normal atmosphere; CA—controlled atmosphere.

> The use of 1-MCP reduces autocatalytic ethylene production and, thus, significantly slows down respiration [27]. The strongest impact of 1-MCP application was found in the last year of the research (Table 4), in which the reduction in fruit mass loss as compared to untreated pears had the highest level of significance in each month of testing. In 2011 and 2012, no differences between 1-MCP-treated and non-1-MCP-treated samples were identified after the first month of storage, whereas the differences were highly significant in the subsequent months.


**Table 3.** Mass loss of non-1-MCP-treated (control) and of 1-MCP-treated 'Conference' pears after storage in normal (NA) and controlled (CA) atmosphere in 2012.

<sup>1</sup> Numbers in parentheses are the standard deviation of the mean (n = 10). <sup>2</sup> *p*-value of F ratio: ns—not significantly different; *\* p* < 0.05; \**\* p* < 0.01; \*\**\* p* < 0.001. Q S1—Quince S1 rootstock; PC—Pyrus caucasica Federov rootstock; PD—Pyrodwarf rootstock. NA—normal atmosphere; CA—controlled atmosphere.

**Table 4.** Mass loss of non-1-MCP-treated (control) and of 1-MCP-treated 'Conference' pears after storage in normal (NA) and controlled (CA) atmosphere in 2013.



**Table 4.** *Cont.*

<sup>1</sup> Numbers in parentheses are the standard deviation of the mean (n = 10). <sup>2</sup> *p*-value of F ratio: ns—not significantly different; *\* p* < 0.05; \**\* p* < 0.01; \*\**\* p* < 0.001. Q S1—Quince S1 rootstock; PC—Pyrus caucasica Federov rootstock; PD—Pyrodwarf rootstock. NA—normal atmosphere; CA—controlled atmosphere.

> However, it was the gaseous composition of the storage atmosphere which had by far the greatest impact on the mass loss during storage. During respiration, sugar and oxygen are combined to produce carbon dioxide and water, the excess of which is transpired into the environment, thus resulting in fruit mass loss [8,11]. The composition of gases in the storage atmosphere strongly influences the rate of fruit respiration [12]. Reducing the oxygen level and increasing the carbon dioxide level slow down respiration and, along with it, the consumption of respiration substrates. This study, during which the oxygen content was reduced to 2%, and the carbon dioxide content was increased to 1%, confirmed the beneficial effect of CA in each year and after each month of storage. This impact was highly significant in each year of the study. Of all the three main factors, the influence of the gaseous composition of the storage atmosphere on fruit mass loss had the highest level of statistical significance.

> Mass loss during storage might also have been caused by parthenocarpy, and 'Conference' pear is known for producing a lot of parthenocarpic fruit in years of adverse weather conditions. It was observed in some earlier studies that parthenocarpy and the number of seeds produced in pears affected both their quality and storability [7].
