Monitoring the viability of citrus rootstocks seeds stored under refrigeration

Abstract

-The citrus nursery tree is produced through the bud grafting process, in which rootstock is usually grown from seed germination. The objective of this research was to evaluate, in two dissimilar environmental conditions, the viability and polyembryony expression of five citrus rootstocks seeds stored in different periods under refrigeration. The rootstock varieties evaluated were: Rangpur lime (Citrus limonia Osb. cv. Limeira), Trifoliate orange (Poncirus trifoliata Raf. cv. Limeira), Citrumelo (P. trifoliata x C. paradisi Macf. cv. Swingle), Sunki mandarin (C. sunki Hort. ex Tanaka) and Volkamer lemon (C. volkameriana Ten. & Pasq. cv. Catania 2). The experimental design was the randomized blocks in a 11 x 5 x 2 factorial scheme, evaluating from time zero to the tenth month of storage, the five varieties of rootstock in two environments: germination and growth B.O.D type chamber (Biological Oxygen Demand -Eletrolab Brand Model FC 122) at 25 °C; and greenhouse seedbed with partial temperature control (22 °C to 36 °C) and humidity control (75-85%). The plot had 24 seeds in four replicates, using trays with substrate in greenhouse and Petri dishes with filter paper in B.O.D. chamber. The seed germination rate and polyembryony expression were evaluated monthly. It was concluded that Trifoliate and Citrumelo Swingle seeds can be stored for up to seven months, while Volkamer lemon, Rangpur lime and Sunki seeds can be stored for up to ten months. The polyembryony expression rate was slightly higher when measured in greenhouse than in B.O.D. chamber and remained stable in both environments until the seventh month, from which dropped sharply. Citrumelo Swingle seeds expressed the highest polyembryony rate (18.8%), followed by Rangpur lime and Volkamer lemon (average value of 13.7%), Sunki (9.4%) and Trifoliate (3.2%). Despite some differences among varieties, the viability of rootstock stored seeds can be monitored either in the greenhouse or in B.O.D. germination chamber, the latter being the faster and more suitable method.

Swingle citrumelo seed vigor and storability associated with fruit maturity classes based on RGB parameters

“…This germination is comparable to the results from Carvalho and Silva (2013) and Siqueira et al (2002), and is also near the expected standard germination of citrus, usually less than 85 % (Carvalho et al, 2002;Ono et al, 1995;Rodrigues et al, 2010). Although similar in germination, seeds extracted from G fruits showed significantly lower vigor compared with Y fruits at 0-month storage.…”

“…Water condensation was observed inside the waterproof package after 5 months of storage, which is considered a high humid condition that could promote seed deterioration. Previous research reported that periodic package opening during storage was necessary to avoid problems with water condensation (Carvalho and Silva, 2013). Here, despite using a similar package during the entire storage period, the highest level of decayed seeds occurred in seeds extracted from Y fruits compared to seeds from G, GY fruits and the control seeds.…”

Radiographic analysis for the evaluation of polyembryony in Swingle citrumelo seeds

“…Furthermore, it interfered in the percentage of polyembryony (7% to 24%), which was lower than that observed by the X-ray method (49% to 62%). Carvalho and Silva (2013) also verified that the mean percentage of polyembryony of Swingle citrumelo seeds was 18.84%.…”

Physiological quality of citrandarins, Poncirus trifoliata and Sunki mandarin seeds

“…There was no significant difference among evaluated varieties. According to Chochemore (1993) According to Carvalho and Silva (2013), trifoliate orange seeds and its hybrids are more sensitive to storage than those of other rootstocks used in the production of citrus seedlings in Brazil and may be considered recalcitrant, i.e., desiccation intolerant with short longevity, in contrast to orthodox ones (Zucareli et al, 2009). In the present work, the maintenance of seed water content above 20% and cold chamber storage with controlled temperature and relative humidity and the use of high density polyethylene (HDPE) plastic bags, which does not allow gas exchanges, prevented seeds from losing germination rate.…”