Seed crops are characterized by relatively low cultivation surface but high economic value. The total surface devoted to the production of seeds in Italy in 2016 was over 37,000 ha with an increase of more than 10,000 ha when compared to 2014 [
1,
2]. In 2014, onion was the first crop in terms of cultivated area, after coriander, with a consistent drop in 2016 from 1700 ha to 980 ha. Three regions hold the primacy: Emilia Romagna, Marche and Puglia with respectively 34%, 24%, 11% of the total cultivated surface [
2]. Marche region is the second producer in Italy with an increased surface of about 9000 ha (from 7000 in 2014) [
1]. As described by Gaikwad et al. [
3] the most common method used to produce onion seeds is the “bulb to seed” method. According to this method, the production is divided into two steps, based on the biyearly physiological characteristics of onion. In the first year, onion mother-bulbs are produced in nurseries starting from seeds. Subsequently, mother-bulbs are sorted and transplanted in the following year to produce seeds [
3]. Seed crops are highly specialized and the production requires many steps with high economic costs that are labor consuming. From a study of Centro di Ricerca Produzioni Vegetali (CPRV) of Cesena, it emerged that the total cost to cultivate one hectare of onion ranges from 4700 and 7300 euros.
As an overview, transplanting, pests and disease control, harvesting, cutting and threshing are the main expenditure items with percentages of 10–16%, 5–15%, 23–27%, 15–19% and 5–7% respectively [
4]. For this reason, companies have pushed for an ever-greater mechanization of the main production phases in order to minimize time, labor and therefore costs. In recent years, many machines for harvesting have been developed and released in the market. Examples are Spapperi model RC443, onion harvester by Meneguzzo, and onion harvester by Montebelli. These machines have been designed to reduce collection time on large plots and their use is almost exclusively possible on flat ground. The onion seed crops of Marche region are typically cultivated in hilly terrain and on surfaces that hardly exceed two hectares. In these conditions, the aspects of greater economic impact are difficult to be minimize, so companies opted for phases in which environmental conditions have little importance such as threshing. In the past, the most common system employed for onion threshing was the manual one, in which the flower heads, after a drying period, are rubbed between the palm of the operator’s hands to allow the seeds to be released from the capsule. Manual threshing is a long and laborious process which often discourages farmers from cultivating onion due to a lack of skilled labour or the excessive cost. Anyway, onion is still considered an important crop to be valorized [
4]. To limit threshing costs, the practice has shifted to mechanical systems. The first generation of mechanical threshing machines, still widely used, consists of common wheat threshing machines appropriately set. These settings generate excessive variability in seed quality. The second generation of threshing machines is designed and constructed only for plants of horticultural interest of the Liliaceae family [
5,
6]. The principal aim of these machines is the increase of threshing yield without compromising seed quality. Considering that seed crops have the aim of producing breeding material for food crops, seed quality is a critical aspect [
7], essential to ensuring crop success. As stated by the Italian government in the legislative decree number 212–001 [
8], the minimum germination for marketing of onion cannot be less than 70% * (Value related to hybrid seed. For quality declared seed systems of FAO (Food and Agriculture Organization) the minimum percentage for open pollinating onion seeds is 60%), the same value was stated by FAO in quality declared seed system in 2006 [
9]. The market demands a significantly higher germinability. From the point of view of the seed user, the high germination ensures greater propagation efficiency and lesser problems arising from the low plant emergence. Therefore, in the production of seeds, any innovation or variation in the production process should maximize economic convenience without affecting seed quality. Many authors already stated that mechanical damages to seeds can reduce their germination and storability for different species: Phaseolus and pulses [
10,
11,
12,
13]; rice [
14], wheat [
15] and other minor crops [
16]. Despite the fact that the previous information is essential for a correct design of a threshing machine, only few studies analyzed onion. Some authors analyzed the mechanical and physical properties of onion seeds [
17,
18,
19,
20] as static coefficient of friction of seeds in relation to moisture, finalizing the results to thresher manufacture or setting up. Other authors evaluated the effects of operational variables on seed quality parameters, and developed a performance index [
5], others, again, developed the machine and tested the qualitative parameters of the seeds [
6].
The principal aim of the present study is the evaluation of mechanical threshing reliability of a machine employed in Italy through the assessment of standard quality parameters for seeds in comparison with manual threshing.