**3. Symptomatology**

The late blight disease affects all plant parts especially leaves, stem and tubers.

#### **3.1. Leaves**

to other parts of the world mainly through infected seed tubers. The late blight disease caused by oomycete, which was initially reported as *Botrytis infestans* in 1845 by C. Montagne, later on German scientist Anton de Bary renamed as *Phytophthora infestans* (Mont.) de Bary [2]. The entire potato crop across Europe, especially in Ireland, was killed prematurely during 1844–45; leading to worst ever famine the 'Irish Potato Famine' [3]. One million people died of starvation due to that famine and another million migrated to the USA and other parts of the world. The late blight disease was recorded in India for the first time between 1870 and 1880 in the Nilgiri hills [4]. Under subtropical plains particularly in eastern part of the India, it was first observed in 1898–1900 in Hooghly district of West Bengal [5]. In the northern part, it appeared for the first time in 1883 in Darjeeling and subsequently spread rapidly to other adjoining hills [6]. The late blight disease was observed in Khasi hills (North-eastern Region) in 1885, Kumaon hills in 1897 and in Shimla hills (North-western Region) in 1902 [5, 7]. During 1913, it appeared at several places in Assam and Bihar [6, 8–11]. In plains of Uttar Pradesh, it was reported for the first time in 1943 in Dehradun and Meerut [10]. Severe attack of the late blight was observed in Meerut district in 1949, 1950 and 1951 and subsequently in many other districts of Uttar Pradesh [12]. In Punjab, the disease was occurred annually from 1958 to 1963 except during 1961 [13]. Potatoes had been grown in Mahabaleshwar hills and other parts of Maharashtra but late blight was observed there only in 1973 [14]. In Gujarat and Madhya Pradesh, the disease was observed in traces in 1968 and in Rajasthan in 1958 [12]. Afterwards, appearance of late blight disease is regular feature with high disease severity in hill areas

*Phytophthora infestans* causes late blight diseases in potato and tomato crops worldwide. It is not cause only economic losses of yield but also the quality and quantity of the crop. It is a highly researchable pathogen in plant diseases. The worldwide late blight disease is reemerging, therefore this disease is constantly observed by the late blight researchers [15]. The late blight disease is considered emerging disease, it is not only having important in global crop production, but also pose severe risks on a local level, especially on small farms in developing countries [16]. The losses caused by late blight disease, it varied countries to countries, as per their adopted plant protections measures and grown cultivars. The yield losses due to late blight of potato were reported up to 50–70% during the 2007 under favorable environmental condition in Pakistan [17]; however recently Ahmed et al. [18] reported that late blight can induce 100% yield loss under epidemic condition in Pakistan. As far as Indian scenario is concerned, reduction in potato production due to late blight ranged between 5 and 90% depending upon climatic conditions, with an average of 15% across the country [19]. However, recently yield loss was reported, overall basis a range of 10–20% due to late blight in the year 2013–2014 major potato growing sites of the India viz., Uttar Pradesh, West Bengal, Punjab, Karnataka and Uttarakhand [20]. Whenever, disease appeared in epiphytotic form at early stage of the crop yield loss would be more. Tuber yield decline was significantly higher in unmanaged crop, which could go as high as 90% of total productivity in hilly regions. The changing climate pattern is being influenced appearance of late blight as it is occurring every

while in plains disease severity is moderate to high level.

**2. Crop losses**

84 Potato - From Incas to All Over the World

Pale green water soaked spots (2–10 mm) appear mostly on the margin and tips. In moist weather, spots may appear anywhere on the leaves, enlarge rapidly and turn necrotic and black killing the entire leaf instantly. On the corresponding lower side, whitish cottony growth containing millions of sporangia forms around the dead area in a ring pattern (**Figure 1**).

#### **3.2. Stem and petiole**

Light brown lesions develop which elongates and encircles the stem and petioles breaking them and killing the plant/leaves instantly. Stem infection is more severe under high temperature and relative humidity conditions (**Figure 2**). Symptoms of stem blight are observed more in last ten years.

#### **3.3. Tubers**

Rusty brown discoloration of the flesh is the typical symptom of late blight (**Figure 3**). On outside tuber surface, hard depressions with purplish tinge on the sides are a common feature. Normally, late blight infected tubers are hard but associated secondary pathogens may set in soft rot symptoms.

#### **3.4. Field infection**

Generally, late blight appears on lower most leaves of the plant which goes unnoticed from a distance. Slowly, the disease spreads to the middle and then upper leaves. Subsequently it

**Figure 1.** Whitish cottony growth on the lower surface of leaf.

spreads whole plants and near of the plants. The disease spreads faster and the entire crop gets killed as if burnt by fire (**Figure 4**). The heavily infected field gives fetid odor which can be felt

Management of Late Blight of Potato http://dx.doi.org/10.5772/intechopen.72472 87

The late blight infected tubers are the major sources to cause the infection. Moreover, refuse piles and volunteer plants also serve as primary source of disease particularly in the hilly

from a distance.

**4. Disease epidemiology**

**Figure 4.** Late blight affected potato field.

**Figure 3.** Late blight symptom on potato tubers.

**Figure 2.** Late blight symptom on potato stem.

**Figure 3.** Late blight symptom on potato tubers.

**Figure 4.** Late blight affected potato field.

**Figure 1.** Whitish cottony growth on the lower surface of leaf.

86 Potato - From Incas to All Over the World

**Figure 2.** Late blight symptom on potato stem.

spreads whole plants and near of the plants. The disease spreads faster and the entire crop gets killed as if burnt by fire (**Figure 4**). The heavily infected field gives fetid odor which can be felt from a distance.
