**5. Effect of hot water treatment on different vegetables**

Nega et al. [15] stated that even with longer treatment times, hot water treatment with a temperature of 40°C had no significant effect on the seed-borne pathogens. However, on all the crops investigated, hot water treatments at temperatures

50 or 53°C for 10–30 min had a good phytosanitary effect. In the majority of cases, these treatment conditions did not affect seed germination. Therefore, to reduce the effect of higher temperature like 53°C on germination, comparatively shorter treatment time must be used, especially on sensitive crops like cabbage, etc. The treatment of 50°C for 30 min is optimal against *Phoma lingam* on cabbage. They also observed that on crops like carrot, cabbage and parsley treatments at temperatures 50–53°C for 10–30 min gave a good elimination of *Alternaria* species.

In the past, Walker [25] observed complete abolition of *P. lingam* from cabbage seeds with treatment at 50°C for 30 min. Clayton [26] recorded similar results for 25 min as well as for 30 min at 50°C. Bant and Storey [27] showed good effects of hot water treatment against *S. apiicola* on celery in field trials. In the view of lack of alternatives, this treatment has proved to be an efficient method on celery and parsley seeds against the *Septoria* species [28] and that too with well-known yield increase. Due to the rapid spread of bacterial diseases like those caused by *Xanthomonas* species [29], hot water treatment has emerged as an important method to control seed-borne bacterial diseases because of lack of chemical or other well-established treatments [30, 31]. The documented efficiency of this treatment on cabbage and cauliflower against *X. campestris* pv*. campestris* is between 25 and 90%. The treatments differ between 50°C for 10–60 min [32–34] and 52°C for 30 min [35].

Melanie et al. [36] demonstrated the efficiency of hot water treatment method in reducing bacterial diseases like bacterial spot and bacterial canker in tomato under greenhouse as well as open-field conditions. They also observed that after treating, seedlings from the same seed lots with hot water did not get diseased in the greenhouse or fields. In plots/fields established from hot water-treated seed, the occurrence of bacterial canker was less extensive, and yields were higher than the plots/fields established from non-treated seeds. Also, fruits from non-treated seeds were considerably smaller than fruits from treated seeds. Reduced infection frequency of bacteria responsible for bacterial canker and bacterial leaf spot was observed in tomato seeds after hot water treatment with increased fruit size and yield.

Hot water treatment of seeds of okra (*Abelmoschus esculentus*) at 52°C for 30 min resulted in the improved crop, both in greenhouse and field conditions. The improvement was with respect to increase in fruit number, leaf number, fruit length and girth, total number of seeds per fruit, seed weight and plant biomass. The hot water treatment of seeds also reduced the frequency of mycoflora infection in the seeds, hence enhancing the vigour index and germination percentage of the seedlings [37]. After soaking carrot seeds in hot water at 52°C for 25 min, the bacterial pathogen (*Xanthomonas hortorum* pv. *carotae*) in and on the carrot was killed [38]. On the other hand, Nandini and Shripad [39], observed that hot water treatment at 52°C for 10 min was effective in controlling the bacterial blight of cowpea with minimum number of infected seedlings and percentage of seedling infection. Germination was also not much affected as compared to control (58 vs. 76.00%).

The effects of hot water treatments of carrot seeds on seed-borne fungi, germination, emergence and yield were studied by Hermansen et al. [40] where the seeds infected with *Alternaria dauci* were hot water treated at temperature ranging from 44 to 59°C at intervals of 5°C for periods of 5–40 min. Treatment of carrot seeds with hot water at 44, 49 and 54°C improved germination rate and reduced the occurrence of *A. dauci*. Hot water treatment at 54°C for 20 min inhibited *A. dauci* without negatively affecting germination rate or yield. Ranganna et al. [41] demonstrated that the potato tubers can safely be stored without sprouting for 12 weeks at 8 or 18°C, if treated with 57.5°C hot water for 20–30 min.

**47**

**Table 1.**

*Hot Water Seed Treatment: A Review*

needs to be investigated (**Table 1**).

Tomato (*Lycopersicon esculentum*)

Bean (*Phaseolus vulgaris*)

(*Pisum sativum*)

Cabbage, cauliflower (*Brassica oleracea*)

Carrot (*Daucus carota*)

Pumpkin (*Cucumis pepo*)

*Thermotherapy to free seeds from pathogenic bacteria.*

**Host Thermotherapy tested**

Tomato Soaking infected

Hot water treatment at 53, 54 and 55°C for 10–60 min

seeds 30 min in hot water at 56°C

Hot water treatments: 50°C for 45–60 min

Dry heat at 65°C for 72 h and soaking in water at 55°C for 15 min

are subjected to hot water treatment at 48°C for 60 min

Hot water treatment at 50°C for 30 min

Hot water treatment (52°C for 10 min)

Hot water treatment at 54 and 56°C for 30 min

Tomato Infected seeds

**Causal agent**

*Clavibacter michiganensis* subsp. *michiganensis*

*C. m*. subsp. *michiganensis*

*P. s.* pv. *phaseolicola*

*P. s.* pv. *tomato*

*Xanthomonas campestris* pv. *campestris*

*X. c.* pv. *carotae*

*X. c.* pv. *cucurbitae*

*Adopted from Grondeau et al. [52].*

*P. s.* pv. *pisi* Pea

*DOI: http://dx.doi.org/10.5772/intechopen.91314*

Hot water treatment of seeds was also observed to be helpful in controlling seedborne pathogens in sweet pepper. Aguilar et al. [42] observed that hot water treatment of bell pepper at 45°C for 15 min or 53°C for 4 min before storing them at 8°C reduced the occurrence of fungal infections. Several hot water treatments of bell pepper seeds resulted in considerable drop-off in seed viability but had no effect on seed vigour [43]. No study can be found in the literature that attempted to arrive at the optimum time-temperature combination for sweet pepper. Therefore, the effect of hot water treatments of sweet pepper seeds on seed viability and seedling vigour

**Result Ref.**

Bryan [44]

Shoemaker and Echandi [45]

Tamietti [46]; Tamietti and Garibaldi [47]

Grondeau et al. [48]

Devash et al. [49]

Shekhawat et al. [34]

Ark and Gardner [50]

Moffett and Wood [51]

Germination remained unaffected up to 55°C for 30 min; bacteria were recovered after 30 min at 53 and 54°C and not after

Plants develop significantly less disease than when no seed treatment is used; seed germination is slightly

Reduction of bacterial number by 98–l00% but 45% reduction in seed germination for 60 min soaking with naturally infected seeds

Significant reduction of pathogen contamination but germination lowered 5–20%

Pathogens are killed, and germination is not affected

Pathogens are eliminated successfully by this treatment to prevent seedling

Can prevent pathogen

Greatly reduces the level of seed infestation but does not completely eliminate it

infestation

infestation

40 min

reduced

#### *Hot Water Seed Treatment: A Review DOI: http://dx.doi.org/10.5772/intechopen.91314*

Capsicum

30 min [35].

yield.

50 or 53°C for 10–30 min had a good phytosanitary effect. In the majority of cases, these treatment conditions did not affect seed germination. Therefore, to reduce the effect of higher temperature like 53°C on germination, comparatively shorter treatment time must be used, especially on sensitive crops like cabbage, etc. The treatment of 50°C for 30 min is optimal against *Phoma lingam* on cabbage. They also observed that on crops like carrot, cabbage and parsley treatments at temperatures

In the past, Walker [25] observed complete abolition of *P. lingam* from cabbage seeds with treatment at 50°C for 30 min. Clayton [26] recorded similar results for 25 min as well as for 30 min at 50°C. Bant and Storey [27] showed good effects of hot water treatment against *S. apiicola* on celery in field trials. In the view of lack of alternatives, this treatment has proved to be an efficient method on celery and parsley seeds against the *Septoria* species [28] and that too with well-known yield increase. Due to the rapid spread of bacterial diseases like those caused by *Xanthomonas* species [29], hot water treatment has emerged as an important method to control seed-borne bacterial diseases because of lack of chemical or other well-established treatments [30, 31]. The documented efficiency of this treatment on cabbage and cauliflower against *X. campestris* pv*. campestris* is between 25 and 90%. The treatments differ between 50°C for 10–60 min [32–34] and 52°C for

Melanie et al. [36] demonstrated the efficiency of hot water treatment method in reducing bacterial diseases like bacterial spot and bacterial canker in tomato under greenhouse as well as open-field conditions. They also observed that after treating, seedlings from the same seed lots with hot water did not get diseased in the greenhouse or fields. In plots/fields established from hot water-treated seed, the occurrence of bacterial canker was less extensive, and yields were higher than the plots/fields established from non-treated seeds. Also, fruits from non-treated seeds were considerably smaller than fruits from treated seeds. Reduced infection frequency of bacteria responsible for bacterial canker and bacterial leaf spot was observed in tomato seeds after hot water treatment with increased fruit size and

Hot water treatment of seeds of okra (*Abelmoschus esculentus*) at 52°C for 30 min resulted in the improved crop, both in greenhouse and field conditions. The improvement was with respect to increase in fruit number, leaf number, fruit length and girth, total number of seeds per fruit, seed weight and plant biomass. The hot water treatment of seeds also reduced the frequency of mycoflora infection in the seeds, hence enhancing the vigour index and germination percentage of the seedlings [37]. After soaking carrot seeds in hot water at 52°C for 25 min, the bacterial pathogen (*Xanthomonas hortorum* pv. *carotae*) in and on the carrot was killed [38]. On the other hand, Nandini and Shripad [39], observed that hot water treatment at 52°C for 10 min was effective in controlling the bacterial blight of cowpea with minimum number of infected seedlings and percentage of seedling infection. Germination was also not much affected as compared to control (58 vs. 76.00%). The effects of hot water treatments of carrot seeds on seed-borne fungi, germination, emergence and yield were studied by Hermansen et al. [40] where the seeds infected with *Alternaria dauci* were hot water treated at temperature ranging from 44 to 59°C at intervals of 5°C for periods of 5–40 min. Treatment of carrot seeds with hot water at 44, 49 and 54°C improved germination rate and reduced the occurrence of *A. dauci*. Hot water treatment at 54°C for 20 min inhibited *A. dauci* without negatively affecting germination rate or yield. Ranganna et al. [41] demonstrated that the potato tubers can safely be stored without sprouting for 12 weeks at

8 or 18°C, if treated with 57.5°C hot water for 20–30 min.

50–53°C for 10–30 min gave a good elimination of *Alternaria* species.

**46**

Hot water treatment of seeds was also observed to be helpful in controlling seedborne pathogens in sweet pepper. Aguilar et al. [42] observed that hot water treatment of bell pepper at 45°C for 15 min or 53°C for 4 min before storing them at 8°C reduced the occurrence of fungal infections. Several hot water treatments of bell pepper seeds resulted in considerable drop-off in seed viability but had no effect on seed vigour [43]. No study can be found in the literature that attempted to arrive at the optimum time-temperature combination for sweet pepper. Therefore, the effect of hot water treatments of sweet pepper seeds on seed viability and seedling vigour needs to be investigated (**Table 1**).


#### **Table 1.**

*Thermotherapy to free seeds from pathogenic bacteria.*
