The Curcuma longa L. genetic germplasms used for evaluation of growth characteristics comprised a total of 9 germplasms (Table 1). The materials were collected in Korea, China, and Japan and was provided from the National Agrobiodiversity Center (Jeonju, Korea). These were compared with C. longa cultivated in Jindo of Jeollanamdo as a control, which is known as local species (Jindo henceforth). In addition, C. longa seed rhizomes were divided into three or four for evaluation of different storage conditions as outlined below.

The test field formed ridges and covered with black plastic bags after the compost was applied using basal fertilization at a total of 4,000 ㎏ per 10 a, considering the soil fertility. The experiment plot was arranged by the randomized complete block design with triplicate. For planting density, furrow spacing was 30 ㎝ in the 90 ㎝ ridges, with 20 ㎝ of plant intervals. The yield was converted to the yield per 10 a after harvesting in 1 m² experiment plot.

C. longa germplasms were cultivated in a National Institute for Horticulture and Herbal Science (NIHHS) experimental field located in Eumseong according to the standard cultural practices. The emergence rate was investigated after 50 days.

The harvested C. longa plants were examined for agronomic characteristics including plant height, leaf length, leaf width, finger rhizome weight, tuberous root weight, etc. The underground portion was also divided into 2 sections and examined (Fig. 1). Investigations were performed from 2015 to 2016 and three independent experiments were performed, representing biological replicates. All data had shown the average of 2 years.

Fig. 1.  Characters of the underground portion of C. longa.

A; stem width, B; finger rhizome, C; root, D; tuberous root.

Rhizomes were placed in a paper bag and a plastic basket, respectively. And they were stored at 4℃, 10℃, 15℃, and 24℃ (room temperature, RT hereafter) for 30, 60, and 90 days.

The conventional storage method (in sealed polyvinyl bags at 4℃, sprayed with water every 2 days) was compared as a control. Every 30 days, the loss of fresh weight, the level of fungal contamination, and sprouting rate were recorded. This experiment had a randomized complete block design. Three independent experiments were performed, representing biological replicates.

Statistical significance of the results was evaluated using One-way ANOVA for comparisons between multiple groups. All calculations were performed using SPSS software Version 22.0 (IBM Co., Armonk, NY, USA). Differences were considered statistically significant at a p value of < 0.05.

To develop new Curcuma longa L. varieties with improved yield and quality and adapted to a Korean cultivation environment, growth characteristics including emergence rate for aerial and underground portions of C. longa plants were evaluated.

Fig. 2 showed the appearance of the underground portion of C. longa. Emergence rate was examined from 50 days after rhizome transplantation. The date of sprouting was earlier for CUR02 and CUR03 than for the control Jindo, however, the overall emergence rate was above 95%, indicating that these resources had the high germination rate (Table 2).

Fig. 2.  Characteristics of the underground portion of C. longa germplasm.

(A); CUR01, (B); CUR02, (C); CUR03, (D); CUR04, (E); CUR05, (F); CUR06, (G); CUR07, (H); CUR08, (I); CUR09.

There was no significantly difference among 9 germplasms during the initial growth stage, while during the later growth stage, CUR04 had the longest plant height. The weight of the aerial portion was 584.1, 577.5, and 610.3 g/plant in CUR03, CUR04, and CUR06, respectively, which were higher than that of other germplasms (Table 3).

Yield per unit area was determined by calculating the number of plants and the weight of root, finger rhizome, and tuberous root. The weight of finger rhizome among individuals in CUR02, CUR03, and CUR06 was 222.9, 222.5, and 225.9 g/plant, respectively, which were higher than those of other groups. The tuberous root weight was the highest in CUR04, which was 23.5 g (Table 4).

On the other hand, when compared to the yield per 1 m², a yield of finger rhizome was significantly higher in CUR09 (3.4 ㎏/m²), CUR01 (3.3 ㎏/m²), and CUR06 (3.3 ㎏/m²), and that of tuberous root was significantly higher at CUR04 (678.7 g/m²) among 9 germplasms (Table 5). However, there was no significant correlation between finger rhizome and tuberous root, it is considered that the yield was decided by individual characteristics or environmental difference.

Assessing genetic resources is considered to be crucial for the genetic improvement of crops. Evaluation of genetic diversity assists in improving the understanding of the genetic background and in demonstrating the breeding value of different germplasm lines.

Plant height and number of leaves have been reported to be determinants of yield potential in individual genotypes in the context of improving turmeric crops (Narayanpur and hanamashetti, 2003).

Therefore our study might be used as fundamental data for breeding variety through the evaluation of the agronomical characteristics of collected C. longa.

This study was conducted to determine the optimal conditions for storage of rhizomes during the winter season. Fresh weight loss, decomposition rate attributed to fungi and sprout rate were evaluated according to the storage containers and temperature.

When rhizomes were stored in a polyvinyl bag at 4℃, as in a conventional method, fresh weights increased due to water absorption. However, when stored in a paper bag and basket container, there was no significant change. At 10℃ and 15℃, there was no remarkable difference or a slight decrease whereas at RT conditions (24℃), fresh weight markedly decreased when stored in paper bags and basket containers (Fig. 3). These results suggest that paper bags and basket containers are better than polyvinyl bags for rhizome storage.

Fig. 3.  Changes in fresh weight (g) of C. longa rhizome exposed to different storage conditions.

The storage duration of C. longa rhizome was 30 days, 60 days, and 90 days, respectively, which shown (A), (B), and (C). Data are shown as means ± SD from three independent biological replicates. ^*Means with the same letter are not significantly different according to Duncan’s Multiple Range Test (DMRT, p < 0.05).

When C. longa rhizomes were stored at 4℃ in a polyvinyl bag, fungal decomposition rate was significantly higher, suggesting that fungal growth occurred due to the addition of water (Fig. 4). When ginger rhizomes were stored in polyethylene file, the weight loss ratio was lower than that of the control (untreated) rhizomes; however, decomposition rate and incidence of fungi were higher (Choi and Kim, 2001). Bambirra et al. (2002) also reported that polyethylene bags were not suitable material for storage of the ground turmeric due to allowing absorption of moisture. This result was shown the same tendency to our present study, which rhizomes stored in polyvinyl bag were absorbed moisture and it induced the fungal decomposition.

Fig. 4.  Incidence of fungal decomposition in C. longa rhizome exposed to different storage conditions.

The storage duration of C. longa rhizome was 30 days, 60 days, and 90 days, respectively, which shown (A), (B), and (C). Data are shown as means ± SD from three independent biological replicates. ^*Means with the same letter are not significantly different according to Duncan’s Multiple Range Test (DMRT, p < 0.05).

Among various physiological factors affected by storage, sprouting is considered the most noticeable symptom of deterioration in the case of many tuber crops (Thomas, 1988; Jaleel et al., 2007). C. longa rhizome sprouting was observed during storage at RT conditions (Fig. 5), induced by the higher temperature. These results indicate that 4℃ and RT conditions are not suitable for rhizome storage due to risk of fungal decomposition (Fig. 6) and sprout emergence, respectively. Thus, these results suggest that C. longa rhizomes remain stable when stored at a temperature between 10℃ and 15℃ in a paper bag and basket container.

Fig. 5.  Sprouting rate in C. longa rhizomes exposed to different storage conditions.

The storage duration of C. longa rhizome was 30 days, 60 days, and 90 days, respectively, which shown (A), (B), and (C). Data are shown as means ± SD from three independent biological replicates. ^*Means with the same letter are not significantly different according to Duncan’s Multiple Range Test (DMRT, p < 0.05).

Fig. 6.  The contamination of fungi after storage of C. longa rhizome with different storage temperatures and containers at 90 days.

Arrows means the contamination of fungi after storage. C. longa rhizome was stored at 4℃ in polyvinyl bag as a practice method (A), 10℃ in paper bag (B), 10℃ in plastic basket (C), 15℃ in paper bag (D), 15℃ in plastic basket (E), respectively.

Similarly, tissue softening, root discoloration, and decay were observed in ginger rhizomes stored below 12℃ (Akamine, 1962). Lim et al. (2013) reported that the optimal storage temperature for C. longa rhizomes was above 10℃. This is similar to the results of our study. Taken together, these results suggest that temperatures between 10℃ and 15℃ provide suitable storage conditions for rhizomes without resulting in chilling-damage.

Harvested roots, tuber, and bulb crops demonstrated decreased weight and decomposition during the storage period; therefore, a simple and effective curing process is required for these plant parts (Cantwell and Kasmire, 1992). Curing protects the rhizomes from contamination at the cutting stage, and controls respiration, moisture transpiration, and sprout development (Salunkhe and Desai, 1984). However, sometimes curing introduces more fungi associated with cutting injury from the harvesting process (Kim et al., 2012). In a study of weight loss and sprouting control in ginger rhizomes, waxing was not shown to reduce moisture content (Paull et al., 1988). Therefore, C. longa rhizomes need to be stored without curing similar to ginger.

In this study, 9 lines of C. longa were evaluated to provide breeding materials for suitable variety in Korea. Based on growth characteristics, among 9 germplasms, the weight of finger rhizome on CUR02, CUR03, and CUR06 were higher than that of others. In addition, CUR09 was shown the high tendency of finger rhizome on yield per 1 m², on the other hand, CUR04 was shown the significantly highest yield per 1 m² of tuberous root. Therefore, it suggest that these germplasm such as CUR09 and CUR04 might be selected useful germplasm for breeding material of finger rhizome and tuberous root, respectively. Furthermore, when C. longa rhizome was stored after harvest, there was some problem. To establishment of optimal storage condition, rhizomes were placed to paper bags, plastic baskets, and polyvinyl bag as a control under different condition. There was not observed any evidence of fungal decomposition or sprouting in rhizome which stored in paper bags or plastic basket at 10℃ and 15℃ compared to a polyvinyl bag at 4℃.

These results suggest that the C. longa rhizome will be able to be stably stored under storage temperature of 10℃ to 15℃ in paper bags or plastic baskets.